Microtubule protein preparations from C6 glial cells and their spontaneous polymer formation.

C6 cell tubulin is indistinguishable from hog brain tubulin with respect to its molecular weight, amino acid composition, and colchicine-binding activity. Moreover, microtubule assembly systems from both sources form the same structures: rings, ribbons, tubules, and drug-induced polymers. There is, nevertheless, a difference between the cultured cell and brain systems which lies in the nature of their microtubule-associated accessory proteins. C6 microtubule preparations exhibit few rings at 0 degrees C, have low polymerization yield, and have a low content of accessory proteins. The addition of brain accessory proteins enhances the numbers of rings, and the yield of microtubules, to levels comparable with those of brain preparations. The polymerizing ability of C6 microtubule protein decays much faster than that of brain, but it can be restored by the addition of brain accessory protein. The results suggest that C6 accessory proteins are more labile than their brain counterparts.

Asynchronous appearance of newly synthesized histone H1 subfractions in HeLa chromatin.

Incorporation of radioactive alanine into chromatin-bound subfractions of H1 histone was studied in HeLa cells synchronized by the double thymidine block technique. The subfractions were resolved into three chromatographic peaks by Biorex-70. In the period 5-7 h after release from the thymidine block, peaks I and III showed twice as much incorporation as they did in the period 1-3 h after release, whereas peak II showed three times the incorporation at 5-7 h that it did at 1-3 h. Thus, the H1-histone subfraction in peak II appears in chromatin somewhat later in S phase than do the subfractions in Peaks I and III.

Histone structure: asymmetric distribution of lysine residues in lysine-rich histone.

Structural studies on a very lysine-rich histone show that the carboxyl-terminal half of the molecule is enriched in lysine (and proline). which suggests that it is a site for binding to DNA. The amino-terminal half. containing most of the acidic residues. resembles small, nonhistone proteins and so might have specificity for factors other than DNA.

Differential scanning calorimetry of nuclei as a test for the effects of anticancer drugs on human chromatin.

Differential scanning microcalorimetry of nuclei from cultured cells revealed differences between antitumor drugs in potency and mechanism. Scanning calorimetry of nuclei showed four structural transitions as the temperature was raised from 25 to 120 degrees C. Transitions II (76 degrees C), III (88 degrees C), and IV (105 degrees C), respectively, characterize the denaturation of the nucleosome, the unstacking of bases in nicked DNA after release from the nucleosome and unstacking in the released intact, supercoiled DNA. Nuclei from human epithelial cells treated with the DNA strand breakers bleomycin and streptonigrin showed an increase in transition III at the expense of transition IV. The effect was dose dependent. At intermediate times of treatment a substantial portion of the chromatin melted between the temperatures of transitions III and IV and this was taken to represent intact supercoiled DNA in which base-pairing had been weakened by loss of some bases. Treatment of cells with the alkylating agents N-nitroso-N-methylurea and mitomycin C gave results similar to those of the strand-breaker antitumor drugs, except that they were less potent. Irradiation by UV gave similar effects. The effects of intercalating drugs were quite distinct from those produced by strand breakers or alkylators. Nuclei from cells incubated with increasing doses of actinomycin D or ethidium bromide gave calorimetric scans that indicated progressive denaturation of the nucleosome and a concomitant stabilization of supercoiled DNA. The loss of transition IV during drug treatment was correlated with the loss of cellular capacity to divide, regardless of which drugs were used.

Fractionation of chromatin fragments on columns of Biogel A50-m at different salt concentrations.

Nuclease fragmented chromatin was chromatographed on Biogel at various NaCl concentrations. The yield of eluted chromatin, and its H1/core histone ratio was minimal at 0.18 M NaCl where the ratio of H1 subtypes H1c/H1ab was maximal. Therefore, the eluted material was aggregation-resistant chromatin while aggregatable chromatin remained on the columns. Previous results were interpreted as H1 depletion of chromatin by ion-exchange properties of Biogel, but the primary phenomenon is now seen as a separation of classes of chromatin that differ in sensitivity to salt-induced aggregation. At very low salt concentrations, Biogel chromatography can be used without concern for H1 depletion.

Histone H1(0) is distributed unlike H1 in chromatin aggregation.

Non-uniform distribution of H1 histone in bovine thymus chromatin was demonstrated previously. Two classes of chromatin differ in aggregation properties and histone content. The class aggregatable by physiological saline is enriched in H1, especially H1ab, the variant known to be most powerful in condensing DNA. Now, the distribution of H1 subtypes is reported for brain chromatin, where H1ab and H1c were distributed as in thymus. In contrast, H1(0) preferred neither the aggregatable chromatin nor the aggregation-resistant class. It is suggested that H1(0) is uniformly distributed with regard to euchromatin and heterochromatin, whereas H1 is concentrated in heterochromatin.

Induction of histone H1(0) differs with different treatments among different cell lines.

Histone H1(0) is an H1 subfraction whose level on the chromatin is inversely correlated with the mitotic index of the cell. We investigated the increase in H1(0) in 6 cell lines when cell division was blocked by 4 methods: 5 mM butyrate, 2% DMSO, serum withdrawal or density inhibition. The 6 cell lines (HeLa S1 and S3, CHO, 3T6, NIE-115 and Vero) responded differently to the treatments as regards the amount of increase in H1(0) and comparisons among the lines reveal no obvious similarities between the lines in the differential effects of the various treatments on H1(0) levels.

Prognostic significance of skin involvement from mucosal tumors of the head and neck.

OBJECTIVE: To examine the hypothesis that skin involvement from mucosal squamous cell carcinoma of the head and neck is a prognostic indicator of a poor outcome. DESIGN: Retrospective review of cases and statistical assessment of median survival times. PATIENTS: Patients with mucosal squamous cell carcinoma of the head and neck. Fifteen patients had direct skin extension and 11 patients had intradermal lymphatic spread. SETTING: University medical center. RESULTS: Direct skin involvement was a prognostic sign of poor outcome but was less ominous than skin involvement by intradermal lymphatic spread. The patients with direct involvement had a 7-month median survival; those with lymphatic spread had a 3-month median survival. At 3 years, all but one patient had died. Involvement of facial skin was better prognostically for duration of survival than was involvement of neck skin. Surgical resection of the involved skin in half of the patients extended palliation 20 months beyond the median survival of the other patients. CONCLUSIONS: Skin involvement from mucosal squamous cell carcinoma of the head and neck indicates a poor prognosis, but resection offers short-term palliation.

Gunshot wounds to the mandible and midface: evaluation, treatment, and avoidance of complications.

As American society becomes progressively violent, an ever-increasing number of gunshot wounds are being seen across the United States. Particularly challenging are injuries that involve the mandible and midface, not only because of problems with reconstructing bone and soft-tissue defects but also because of emergent problems with airway obstruction and neurovascular compromise. We present 40 cases of gunshot wounds to the mouth, mandible, and maxilla treated at Wake Forest University Medical Center during the past 7 years. The focus of this retrospective analysis is on emergency evaluation and treatment, complications encountered, and operative techniques used for reconstruction. Special emphasis is placed on recognizing and avoiding the complications of these injuries.