Genome sequences of Mycoplasma alligatoris A21JP2T and Mycoplasma crocodyli MP145T.

Mycoplasma alligatoris and Mycoplasma crocodyli are closely related siblings, one being highly virulent and the other relatively attenuated. We compared their genomes to better understand the mechanisms and origins of M. alligatoris' remarkable virulence amid a clade of harmless or much less virulent species. Although its chromosome was refractory to closure, M. alligatoris differed most notably by its complement of sialidases and other genes of the N-acetylneuraminate scavenging and catabolism pathway.

Expression and processing of the AIDS virus reverse transcriptase in Escherichia coli.

The ability to express the genes of pathogenic human viruses, such as the acquired immune deficiency syndrome (AIDS) virus (also called human immunodeficiency virus) in bacterial cells affords the opportunity to study proteins that are ordinarily difficult or inconvenient to obtain in amounts sufficient for detailed analysis. A segment of the AIDS virus pol gene was expressed in Escherichia coli. Expression resulted in the appearance of reverse transcriptase activity in the bacterial cell extracts. The extracts contained two virus-related polypeptides that have the same apparent molecular weights as the two processed forms of virion-derived reverse transcriptase (p66 and p51). The formation of these two polypeptides depended on the coexpression of sequences located near the 5' end of the pol gene, a region that is thought to encode a viral protease. This bacterial system appears to generate mature forms of the AIDS virus reverse transcriptase by a proteolytic pathway equivalent to that which occurs during virus infection of human cells.

Daily changes in hypothalamic gene expression of neuropeptide Y, galanin, proopiomelanocortin, and adipocyte leptin gene expression and secretion: effects of food restriction.

The participation of hypothalamic neuropeptide Y (NPY)-, galanin (GAL)-, and opioid-producing neurons in the restraint on food intake exerted by adipocyte leptin has recently been recognized. To further understand the interplay between the central appetite-stimulating- and peripheral appetite-inhibiting signals in the management of daily food intake, we have examined the daily patterns in expression of the hypothalamic neuropeptides and leptin receptor (R) and adipocyte leptin gene expression and secretion in freely feeding (FF) rats. These analyses were extended to determine the impact of food restriction (FR) to 4 h daily for 4 weeks. Groups of FF and FR rats were killed at 4-h intervals during a 24-h period, and hypothalamic NPY, GAL, POMC, and leptin-R gene expression and leptin gene expression were evaluated by RNase protection assays and serum leptin and corticosterone (CORT) levels were estimated by RIA. The following new findings emerged: 1) In FF rats, hypothalamic NPY messenger RNA (mRNA) levels fluctuated during the course of 24 h with high levels at 0700 h and 1100 h followed by a decrease at 1500 h during the lights-on phase that was sustained throughout the dark phase (1900 h-0500 h) of the light-dark cycle. Hypothalamic GAL and POMC mRNA also displayed daily patterns but with a different time course; GAL and POMC gene expression were elevated 4 h later than NPY mRNA at 1100 h and 1500 h. 2) Although FR to 4 h between 1100 h and 1500 h resulted in maintenance of body weight compared with a steady weight gain in FF rats, the daily patterns of fluctuations in hypothalamic neuropeptide gene expression were abolished. 3) In FF rats, hypothalamic leptin-R and adipocyte leptin gene expression and serum leptin levels displayed a daily pattern temporally different from that of hypothalamic neuropeptide gene expression. Adipocyte leptin mRNA remained low during the lights-on phase but increased at the onset of the lights-off phase (1900 h) and remained elevated through the dark phase. 4) Hypothalamic leptin-R gene expression, like that of adipocyte leptin gene expression, rose abruptly at the onset of nocturnal feeding behavior but receded progressively to low range thereafter. 5) On the other hand, a dichotomy in the daily rise in adipocyte leptin gene expression and leptin secretion was observed in FF rats. Unlike adipocyte leptin mRNA, serum leptin increased at 2300 h, 4 h after initiation of ingestive behavior. 6) In FR rats, adipocyte leptin gene expression fluctuated little over the 24-h period but, as in FF rats, leptin hypersecretion peaked 4 h after initiation of food intake. 7) In both FF and FR rats, increased serum CORT levels preceded serum leptin rise. Overall, these results show that in FF rats, gene expression of hypothalamic appetite stimulating peptides first rise and then fall to nadir during the lights-on phase when leptin levels are in low range; adipocyte leptin mRNA rises before impending ingestive behavior and increased leptin secretion reaching peak manifests itself during nocturnal feeding. The FR regimen, which curtailed the normal body weight gain, abolished these daily fluctuations in gene expression of hypothalamic orexigenic peptides and adipocyte leptin but permitted feeding-associated increased leptin secretion. Thus, it may be important to consider the daily patterns of gene expression and availability of hypothalamic orexigenic peptides in investigations aimed at elucidating the central mechanisms underlying the feedback action of the normal and altered leptin secretion patterns.

Anorectic effects of the cytokine, ciliary neurotropic factor, are mediated by hypothalamic neuropeptide Y: comparison with leptin.

Although ciliary neurotropic factor (CNTF) is a tropic factor in nervous system development and maintenance, peripheral administration of this cytokine also causes severe anorexia and weight loss. The neural mechanism(s) mediating the loss of appetite is not known. As hypothalamic neuropeptide Y (NPY) is a potent orexigenic signal, we tested the hypothesis that CNTF may adversely affect NPYergic signaling in the hypothalamus. Intraperitoneal administration of CNTF (250 microg/kg) daily for 4 days significantly suppressed 24-h food intake in a time-dependent manner and decreased body weight. The loss in body weight was similar to that which occurred in pair-fed (PF) rats. As expected, hypothalamic NPY gene expression, determined by measurement of steady state prepro-NPY messenger RNA by ribonuclease protection assay, significantly increased in PF rats in response to energy imbalance. However, despite a similar loss in body weight, there was no increase in NPY gene expression in CNTF-treated rats. Daily administration of CNTF intracerebroventricularly (0.5 or 5.0 microg/rat) also produced anorexia and body weight loss. In this experiment, negative energy balance produced by both PF and food deprivation augmented hypothalamic NPY gene expression. However, despite reduced intake and loss of body weight, no similar increment in hypothalamic NPY gene expression was observed in CNTF-treated rats. In fact, in rats treated with higher doses of CNTF (5.0 microg/rat), NPY gene expression was reduced below the levels seen in control, freely fed rats. Furthermore, CNTF treatment also markedly decreased NPY-induced feeding. These results suggested that anorexia in CNTF-treated rats may be due to a deficit in NPY supply and possibly in the release and suppression of NPY-induced feeding. The possibility that CNTF-induced anorexia may be caused by increased leptin was next examined. Daily intracerebroventricular injections of leptin (7 microg/rat) decreased food intake, body weight, and hypothalamic NPY gene expression in a manner similar to that seen after CNTF treatment. Leptin administration also suppressed NPY-induced feeding. However, peripheral and central CNTF injections markedly decreased leptin messenger RNA in lipocytes, indicating a deficiency of leptin in these rats; thus, leptin was unlikely to be involved in appetite suppression. Thus, these results show that a two-pronged central action of CNTF, causing diminution in both NPY availability and the NPY-induced feeding response, may underlie the severe anorexia. Further, unlike other members of the cytokine family, suppression of NPYergic signaling in the hypothalamus by CNTF does not involve up-regulation of leptin, but may involve a direct action on hypothalamic NPY neurons or on neural circuits that regulate NPY signaling in the hypothalamus.

Competitive RNA templates for detection and quantitation of growth factors, cytokines, extracellular matrix components and matrix metalloproteinases by RT-PCR.

Detection of low-abundance mRNAs by reverse transcription-polymerase chain reaction (RT-PCR) has become a standard technique to determine gene expression by tissues and cells in culture. The ability to determine relative or absolute copy number of specific mRNAs has been difficult due to inadequate internal standards to control for sample-to-sample variation. The use of a synthetic RNA standard with identical sequences to the PCR primers allows reproducible quantitation between samples and assays. By designing multi-sequence templates, several specific mRNAs can be quantitated using a single template. Addition of multiple templates to a single RT reaction allows the quantitation of a large number of targets from as little as 4 micrograms of total RNA. In this report, we present a series of seven primer/template systems to detect and quantitate 52 specific messages, including 26 growth factors and receptors, 8 extracellular matrix components, 10 matrix-modifying enzymes and their inhibitors and 8 cytokines.

Expression and characterization of recombinant rat placental prolactin-like protein C.

Prolactin-like protein C (PLP-C) is a member of the rat placental family of proteins which are structurally related to pituitary prolactin (PRL). In an effort to characterize the receptor specificity and biological activity of PLP-C, we used a PLP cDNA to express the recombinant protein in a bacterial system. The PLP-C cDNA was modified by oligonucleotide mutagenesis and ligated into a human carbonic anhydrase II (hCAII) expression vector. Following a single step affinity purification, the hCAII-PLP-C fusion protein was digested with enterokinase to release a 25 kDa protein. N-Terminal sequence analysis of the 25 kDa band demonstrated identity with PLP-C. A polyclonal antiserum to the fusion protein cross reacted with seven major proteins in rat placental culture media of which two were the native forms of PLP-C. Recombinant PLP-C was not mitogenic in the Nb2 lymphoma bioassay and did not exhibit high affinity binding to rat PRL receptor. The choice of hCA-II fusion allows for rapid purification of rPLP-C which will aid in further investigation of the biological role of PLP-C.

Neuropeptide Y (NPY) Y1 receptor mRNA is upregulated in association with transient hyperphagia and body weight gain: evidence for a hypothalamic site for concurrent development of leptin resistance.

Microinjection of colchicine (COL), a neurotoxin that blocks axoplasmic flow in the neurons, bilaterally into the ventromedial nucleus (VMN) evokes transient hyperphagia and body weight gain. These shifts in energy balance occurred in conjunction with development of increased sensitivity to neuropeptide Y (NPY), the endogenous orexigenic signal. In order to trace the aetiology of NPY supersensitivity, we have evaluated (1) NPY Y1 and Y5 receptor (R) gene expression in the hypothalamus and (2) the possibility of alterations in the inhibitory action of leptin, a hormone produced by lipocytes. Adult male rats were rendered hyperphagic with bilateral microinjections of COL (4 microg/side) into the VMN. We observed that hypothalamic NPY Y1 mRNA levels, as measured by RNAase protection assay, were significantly increased on day 2 and returned to the control level on day 4 in COL-injected rats. The effects on NPY Y5R mRNA were not as clear cut. Interestingly, serum leptin levels increased in association with the hyperphagia and body weight gain, thereby raising the likelihood of development of resistance to the suppressive effect of endogenous leptin on food intake. Indeed, intracerebroventricular injection of 7 microg human recombinant leptin, a dose that attenuated daily food intake in normal and fasted rats, was completely ineffective in attenuating hyperphagia in COL-treated rats. These results show that transient hyperphagia induced by interruption of signalling in the VMN may be caused by increased sensitivity to NPY, which may be caused, in part, by increased expression of NPY Y1R in hypothalamic sites involved in regulation of ingestive behaviour. Additionally, the observation of increased leptin release and concurrent development of leptin resistance suggest that a normally functioning VMN may be necessary for the central inhibitory effects of leptin on food intake.

Evidence that dark-phase hyperphagia induced by neurotoxin 6-hydroxydopamine may be due to decreased leptin and increased neuropeptide Y signaling.

Hyperphagia and obesity can be experimentally induced in rodents by microinjection of 6-hydroxydopamine (6-OHDA) into the ventral noradrenergic bundle (VNAB) to interrupt efferent catecholaminergic pathways to the hypothalamus. Since hypothalamic neuropeptide Y (NPY) is implicated in the control of ingestive behavior, we evaluated hypothalamic NPY activity in this model of obesity. Adult male rats injected bilaterally with 12 microg of 6-OHDA in the VNAB displayed an enhanced rate of body weight gain and selective dark-phase hyperphagia that started at about 10 days postinjection and persisted for the entire duration of the experiment. NPY gene expression, assessed by ribonuclease protection assay, was significantly higher in the hypothalami of 6-OHDA-treated hyperphagic rats during the dark phase (p < 0.01 vs. levels during the light phase and in control, vehicle-injected rats). We also evaluated gene expression of NPY Y and Y5 receptors, receptor subtypes reported to mediate NPY-induced feeding. The dark-phase increase in NPY mRNA was accompanied by the concomitant upregulation of NPY Y5R gene expression, but not of Y1R mRNA levels. Leptin, the peripheral hormone secreted by adipocytes, is believed to maintain body weight and inhibit food intake, most likely by suppressing hypothalamic NPY activity. Evaluation of leptin gene expression in the epididymal fat revealed that the upregulation of leptin mRNA noted during the dark phase in control rats did not occur in 6-OHDA-treated rats. These observations implied that the normal restraint on NPY and feeding exercised by leptin in control rats may be abrogated in 6-OHDA-treated hyperphagic rats due to insufficient levels of leptin. If so, administration of leptin should inhibit food intake in these rats. Indeed, injection of leptin (2 mg/kg, intraperitoneally (i.p.)) on 2 consecutive days reduced 24-h food intake by 25% and significantly reduced body weight. These results suggest that the nocturnal hyperphagia and resultant obesity induced by 6-OHDA injected into the VNAB may be attributed to leptin deficiency concomitant with increased hypothalamic NPY.

The polyomavirus early promoter: role of proximal promoter elements in the formation of 5' termini in vivo.

Analysis of polyomaviruses with altered early promoter sequences indicates that in vivo (1) the polyomavirus early ATA motif and nearby upstream sequences dictate homogeneity of 5' termini, in contrast to what has been observed in vitro, where the cap site was reported to affect homogeneity of 5' termini (P. Jat, V. Novak, A. Cowie, C. Tyndall, and R. Kamen, 1982, Mol. Cell. Biol. 2, 737-751). (2) Substitution of the polyomavirus ATA motif by the adenovirus 2 major later promoter suppresses minor early 5' termini between the origin and the early cap sites, indicating that these termini are not the result of DNA replication.

Regulation of polyomavirus transcription by large tumor antigen.

We have analyzed the regulation of viral transcription by the large tumor antigen in cells infected by several viable deletion and insertion mutants of polyomavirus. We find that deletion of the early promoter "TATA box" and associated large tumor antigen binding site has only a small effect on the balance of early and late mRNAs. Furthermore, transcription of a polyomavirus containing a heterologous adenovirus promoter in place of the normal TATA box and cap sites is regulated by the large tumor antigen. We conclude that repression of polyomavirus early transcription cannot occur simply by binding of the large tumor antigen to DNA sequences at the site of transcription initiation and must involve the interaction of the large tumor antigen binding at other sites.

Spreading factors of Mycoplasma alligatoris, a flesh-eating mycoplasma.

Mycoplasma alligatoris causes lethal invasive disease of alligators and caimans. A homolog of the nagH gene, encoding a hyaluronidase secreted by Clostridium perfringens, and a C. perfringens hyaluronidase nagI or nagK pseudogene were discovered in the M. alligatoris genome. The nagH gene was detected by PCR in the closest relative of M. alligatoris, Mycoplasma crocodyli, but not in 40 other species representing the Mycoplasma hominis, Mycoplasma pneumoniae, and Spiroplasma phylogenetic clusters. The hyaluronidase activity in the cellular fraction of M. alligatoris and M. crocodyli SP4 broth cultures was equivalent to 10(-16) U of Streptomyces hyalurolyticus hyaluronidase CFU(-1). Negligible activity was present in the cell-free supernatant fraction. No chondroitinase activity was detected. There is also a novel homolog of the nanI gene, which encodes a sialidase secreted by C. perfringens, in the M. alligatoris genome. The signature YRIP and SXDXGXTW motifs and catalytic residues of the clostridial sialidase are conserved in the mycoplasmal gene, but the leader sequence necessary for its secretion by C. perfringens is absent. The gene was not detected by PCR in any other mycoplasma. Potent cell-associated sialidase activity was present in M. alligatoris colonies on agar but not in the cell-free supernatants of broth cultures or in M. crocodyli. The presence of hyaluronidase and sialidase in M. alligatoris is consistent with the rapid invasiveness and necrotizing effects of this organism, and the lack of sialidase in M. crocodyli is consistent with its comparatively attenuated virulence. This genetic and biochemical evidence suggests that the spreading factors hyaluronidase and sialidase, a combination unprecedented in mycoplasmas, are the basis of the virulence of M. alligatoris.

Mutational analysis of human immunodeficiency virus type 1 protease suggests functional homology with aspartic proteinases.

Processing of the retroviral gag and pol gene products is mediated by a viral protease. Bacterial expression systems have been developed which permit genetic analysis of the human immunodeficiency virus type 1 protease as measured by cleavage of the pol protein precursor. Deletion analysis of the pol reading frame locates the sequences required to encode a protein with appropriate proteolytic activity near the left end of the pol reading frame but largely outside the gag-pol overlap region, which is at the extreme left end of pol. Most missense mutations within an 11-amino-acid domain highly conserved among retroviral proteases and with sequence similarity to the active site of aspartic proteinases abolish appropriate processing, suggesting that the retrovirus proteases share a catalytic mechanism with aspartic proteinases. Substitution of the amino acids flanking the scissile bond at three of the processing sites encoded by pol demonstrates distinct sequence requirements for cleavage at these different sites. The inclusion of a charged amino acid at the processing site blocks cleavage. A subset of these substitutions also inhibits processing at the nonmutated sites.

Structure of an inhibitor complex of the proteinase from feline immunodeficiency virus.

The crystal structure of a recombinant form of the proteinase encoded by the feline immunodeficiency virus (FIV PR) has been solved at 2 A resolution and refined to an R-factor of 0.148. The refined structure includes a peptidomimetic, statine-based inhibitor, LP-149, which is an even more potent inhibitor of HIV PR. Kinetic parameters were obtained for the cleavage of five substrates by FIV PR, and inhibition constants were measured for four inhibitors. The structure of FIV PR resembles other related retroviral enzymes although few inhibitors of HIV PR are capable of inhibiting FIV PR. The structure of FIV PR will enhance our knowledge of this class of enzymes, and will direct testing of new proteinase inhibitors in a feline animal model.

Natural variation in HIV-1 protease, Gag p7 and p6, and protease cleavage sites within gag/pol polyproteins: amino acid substitutions in the absence of protease inhibitors in mothers and children infected by human immunodeficiency virus type 1.

Reduced sensitivity of human immunodeficiency virus type 1 (HIV-1) to protease inhibitors is associated with multiple amino acid substitutions in the virus-encoded protease. The combination of changes that contribute to drug resistance is dependent in part upon the amino acid residues comprising protease alleles prior to drug therapy. We analyzed within peripheral blood mononuclear cells from HIV-1-infected mothers and their children viral gag/pol regions, which included p7, transframe p6/p6*, and protease coding sequences, as well as six protease cleavage sites. Sixty protease alleles from 12 individuals differed by at least 3 to as many as 10 amino acids from proteases encoded by molecular clones of HIV-1, indicating that there is no prototype or consensus wild-type HIV-1 protease sequence. Protease variants with a proline at position 63, a substitution associated with resistance to protease inhibitors, appeared in the absence of antiprotease therapy in 7 patients and were transmitted by 2 mothers to their infants. Gag p7 p6 regions were significantly more variable than protease. The p6/p6* region contained length variants and amino acid repeats in both reading frames. Five protease cleavage sites (B, D', D, E, and F) contained highly conserved amino acid sequences in individuals infected by epidemiologically distinct viruses. In contrast, C cleavage sites, localized between Gag p2 and Gag p7, displayed considerable amino acid variability, were unique among groups of infected individuals, and appeared to be related to particular protease alleles. Genetic variability in vivo in protease, in cleavage sites, and in proteins upstream of protease provides the potential to modulate enzyme activity and susceptibility to protease inhibitors.

Sensitive, soluble chromogenic substrates for HIV-1 proteinase.

By replacement of the P1' residue in a capsid/nucleocapsid cleavage site mimic with 4-NO2-phenylalanine (Nph), an excellent chromogenic substrate, Lys-Ala-Arg-Val-Leu*Nph-Glu-Ala-Met, for HIV-1 proteinase (kappa cat = 20 s-1, Km = 22 microM) has been prepared. Substitution of the Leu residue in P1 with norleucine, Met, Phe, or Tyr had minimal effects on the kinetic parameters (kappa cat and kappa cat/Km) determined at different pH values, whereas peptides containing Ile or Val in P1 were hydrolyzed extremely slowly. The spectrophotometric assay has been used to characterize the proteinase further with respect to pH dependence, ionic strength dependence, and the effect of competitive inhibitors of various types.

Identification of lysine decarboxylase as a mammalian cell growth inhibitor in Eikenella corrodens: possible role in periodontal disease.

The pathogenesis of inflammatory periodontal disease was studied by examining the mechanism of HeLa and HL60 cell growth inhibition by cell-free saline-soluble extracts of Eikenella corrodens and bacterial plaque. Previous studies identified a protein (p80) as causing growth inhibition by E. corrodens extracts. After purification by two-dimensional SDS-PAGE, p80 was digested with protease lysC. Amino acid sequences were obtained and backtranslated for use as PCR primers. A 5840 nucleotide sequence containing a lysine decarboxylase gene was obtained from a Sau3 A1 genomic library of E. corrodens DNA. Lysine decarboxylase activity was present at physiologic pH in the E. corrodens extracts containing p80, and also in bacterial plaque. Both extracts caused growth inhibition by depleting lysine from cell culture media through conversion to cadaverine. Adding lysine, or immune goat IgG to a peptide derived from the active site sequence of E. corrodens lysine decarboxylase, retarded lysine depletion and growth inhibition. epsilon-Amino caproic acid specifically enhanced lysine decarboxylase activity at the low lysine concentration in HL60 cell culture media, and also increased the growth inhibition. Thus, lysine decarboxylases such as p80 inhibit growth by removing lysine from mammalian cell culture media. A new role for lysine decarboxylase activity in the microbial aetiology of periodontal disease is discussed.