Expression of recombinant human insulin-like growth factor I in mammalian cells.

In order to develop a suitable mammalian expression system for human insulin-like growth factors (hIGFs) and mutant IGFs, we have constructed several artificial IGF genes, based on a cDNA encoding the IGF-I precursor (153 amino acids). Transient expression experiments using mouse Ltk- cells revealed that the IGF-I gene constructs were efficiently expressed when placed under control of the SV40 Early promoter (SV40E). This resulted in the synthesis and secretion of IGF-I receptor-reactive products. Constructs encoding an IGF-I precursor with a truncated signal peptide of 25 amino acids under control of SV40E promoter or the inducible Drosophila heat shock hsp70 promoter, were used to establish stably transformed CHOdhfr- and mouse L cells. Clones secreting IGF-I were identified by an IGF-I-specific radioreceptor assay. Immunoblot analysis of conditioned media from these clones resulted in the specific precipitation of a protein of 7 kDa identical in size to native IGF-I purified from human serum. After optimization of the expression conditions, the stable cell lines secrete 0.5-2 microgram/10(6) cells of IGF-I. The biological activity of the secreted recombinant IGF-I was shown by its ability to stimulate DNA synthesis in human MCF-7 cells. The results described in this paper indicate that a mammalian expression system, employing CHOdhfr- or L cells, is a useful system for the synthesis of biological active IGF-I.

Isolation, characterization and restriction endonuclease mapping of the Petunia hybrida chloroplast DNA.

A procedure is developed for the isolation of intact chloroplast DNA (ctDNA) from Petunia hybrida. The molecular weight, calculated from contour length measurements, is 96.0 +/- 4.5 x 10(6) daltons. This value is in good agreement with the value of 101.2 x 10(6) daltons that was estimated from the electrophoretic mobilities of restriction endonuclease fragments of ctDNA. Analysis of petunia ctDNA in neutral CsCl gradients revealed the presence of only one type of DNA at a buoyant density of 1.6987 +/- 0.0005 gcm-3. This corresponds with a GC-content of 39.3 +/- 0.5%. A physical map of petunia ctDNA was constructed by using the restriction endonucleases Sal I, Bgl I, Hpa I and Kpn I. The map indicates that petunia ctDNA contains two copies of a sequence in an inverted orientation. The inverted repeat regions have a minimum length of 10 x 10(6) daltons. Hybridization data indicate that part of the inverted repeat regions contain the genes for chloroplast ribosomal RNAs.

Restriction endonuclease analysis of chloroplast DNA in interspecies somatic Hybrids of Petunia.

Restriction endonuclease cleavage pattern analysis of chloroplast DNA (cpDNA) of three different interspecific somatic hybrid plants revealed that the cytoplasms of the hybrids contained only cpDNA of P. parodii. The somatic hybrid plants analysed were those between P. parodii (wild type) + P. hybrida (wild type); P. parodii (wild type)+P. inflata (cytoplasmic albino mutant); P. parodii (wild type) + P. parviflora (nuclear albino mutant). The presence of only P. parodii chloroplasts in the somatic hybrid of P. parodii + P. inflata is possibly due to the stringent selection used for somatic hybrid production. However, in the case of the two other somatic hybrids P. parodii + P. hybrida and P. parodii + P. parviflora it was not possible to determine whether the presence of only P. parodii chloroplasts in these somatic hybrid plants was due to the nature of the selection schemes used or simply occurred by chance. The relevance of such somatic hybrid material for the study of genomic-cytoplasmic interaction is discussed, as well as the use of restriction endonuclease fragment patterns for the analysis of taxonomic and evolutionary inter-relationships in the genus Petunia.

Physical mapping, nucleotide sequencing and expression in E. coli minicells of the gene for the large subunit of ribulose bisphosphate carboxylase from Petunia hybrida.

The Petunia hybrida rbcL gene was identified and located on the physical map within the Sall S9 fragment of the Petunia hybrida cpDNA by heterologous hybridization with the cloned rbcL gene of spinach (pSoc3BE148). In E. coli minicells harbouring the S9 fragment inserted into pBR322, the rbcL polypeptide is synthesized as was shown by molecular weight determination, immunoprecipitation and proteolytic digestion. However, the size of the rbcL polypeptide synthesized in minicells appeared to be dependent on the orientation of the S9 fragment in pBR322. In minicells harbouring the S9 fragment inserted into pBR322 in the clockwise orientation the molecular weight of the rbcL polypeptide is approximately 53 kD, whereas in minicells harbouring the S9 fragment in the opposite orientation, the rbcL polypeptide synthesized has a molecular weight of 52 kD. The difference in molecular weight of the two rbcL polypeptides is the result of transcription and translation into the flanking pBR322 sequences. This is due to the absence of the terminal part (6 codons), including the translation stop codon, of the rbcL gene on the cloned S9 fragment as was determined by nucleotide sequencing. The observed expression of the cloned part of the rbcL gene of Petunia hybrida indicates that the E. coli minicell system can be used as a suitable and convenient system for the identification and physical mapping of chloroplast genes.Comparison of the sequence of the untranslated 3'-end of the rbcL gene of Petunia hybrida with that of Nicotiana tabacum revealed a striking similarity of the region in which stem and loop structures can be formed that are most likely involved in termination of transcription of the rbcL gene. This region appears to be highly conserved in the rbcL genes of P. hybrida, N. tabacum, S. oleracea and Z. mays.

Chloroplast DNAs of Spinacia, Petunia and Spirodela have a similar gene organization.

We have located the positions of the genes coding for the α, ß and ε subunits of the ATPase complex on Spirodela oligorhiza chloroplast DNA by means of heterologous hybridization with Spinacia cpDNA fragments.The overall cpDNA sequence organization of Petunia hybrida and Spirodela was compared. We hybridized well-characterized, cloned Spirodela cpDNA fragments with size fractionated Petunia cpDNA digested by Sall. It appears that the monocotyledonous Spirodela and the dicotyledonous Petunia cpDNA share a common sequence organization around their entire circumference. These observations, together with data reported in the literature, indicate a strikingly similar genetic organization of the chloroplast genome in widely divergent plants.