Molar proportions and relative rates of synthesis of histones in rat testis

The molar proportions and relative rates of synthesis of histones in normal and hypophysectomized rat testis seminiferous epithelial cells were determined. After hypophysectomy the molar proportions of histones H1, H2B and (H2A + protein A24) in seminiferous epithelial cells of rat testis increased while their corresponding variants TH1-x, TH2B-x and X₂ decreased, but the molar proportions of major-class histones (i.e., sum of subfractions) remained relatively constant and similar to the proportions in somatic cells. The apparent molar proportions of the labeled histones, determined immediately after 2-h periods of [³H]leucine incorporation, were much higher relative to H4 than the proportions of total histones determined by dye binding. The values, however, approached the molar proportions of total histones when rats were killed 11 days after the [³H]leucine injection. Two-dimensional gel electrophoresis confirmed that the high initial molar proportions relative to H4 by [³H]leucine incorporation were not due to the possible contamination by highly-labeled non-histone proteins. The specific activity of histone H4 relative to the specific activity of DNA, determined immediately after 3-h periods of [³H]leucine and [¹⁴C]thymidine incorporations was similar to the value when rats were killed 13 days after the injections. It is proposed that histones of seminiferous epithelial cells are synthesized disproportionally relative to H4 and in excess of the quantities required for polynucleosome assembly. The excess histones are subsequently displaced or degraded slowly.     

Isozyme shift in cultured fetal human hepatocytes: a study of pyruvate kinase and phosphofructokinase

Hepatocytes from a 4-month old fetus were cultured for 15 days. We found that fetal hepatocytes contained some R₁ (precursor) form of L-type pyruvate kinase. Culture was associated with a considerable increase of the M₂-type pyruvate kinase activity, but some L-type enzyme could be detected even after 10 days.Isozyme shift of phosphofructokinase seemed to be a progressive rather low phenomenon. Fetal hepatocytes showed an increase of the F-type form and a disappearance of the M-type form during culture. However, by day 10, the L-type enzyme remained predominant; this is in striking contrast with the findings reported on cultured fibroblasts.From these results, pyruvate kinase can be considered as a “strong” marker of cell differentiation, while phosphofructokinase is rather a “weak” marker.     

Purine transport by Malpighian tubules of pteridine-deficient eye color mutants of Drosophila melanogaster

Uptakes of guanine into Malpighian tubules of wild-type Drosophila and the eye color mutants white (w), brown (bw), and pink-peach (p ^p) have been compared. Tubules for each of these mutants are unable to concentrate guanine intracellularly. The transport of xanthine and riboflavin is also deficient in w tubules. The transport of guanosine, adenine, hypoxanthine, and guanosine monophosphate is similar in wild-type and white Malpighian tubules. These data and other information about these mutants make it likely that these pteridine-deficient eye color mutants do not produce pigments because of the inability to transport a pteridine precursor. This view supports the hypothesis that mutants which lack both pteridine and ommochromes do so because precursors to both classes of pigments share a common transport system.This work was supported by Grant GM22366 from NIH.     

Effect of mouse genotype on interferon production

Upon induction with Newcastle disease virus, peritoneal macrophages derived from C57BL/6 mice produced ten times as much interferon as macrophages derived from BALB/c mice. This suggested that the alleles of theIf-1 locus are expressed in vitro by these cells. Further evidence for this was obtained by studying interferon production by peritoneal macrophages derived from seven recombinant inbred and one congenic line: in each case there was complete correlation between in vivo and in vitro phenotype: macrophages fromIf-1^l mice were low producers in vitro, and macrophages fromIf-1 ^h mice were high producers in vitro.