Terminal deoxyribonucleotidyl transferase activity in acute undifferentiated leukemia.

Guanosine, rather than its methylated derivative, was found to be the inverted nucleoside present in the 5′ terminal capping structure of insect oocyte messenger RNA. Since methylation of the terminal guanosine at the 7 position is necessary for the initiation of protein synthesis in eukaryotes, this evidence suggests that the translational inactivity of the mRNA prior to fertilization may be associated with the absence of methylation.     

Separation of two HMM-S1 species from white muscle myosin

Heavy meromyosin subfragment 1 was resolved by chromatography on DEAE-cellulose into two fractions characterized by the nature of the alkali light chains present. It was shown that even in an HMM-S1 preparation with an extensive fragmentation of the heavy chain a polyacrylamide gel electrophoresis analysis differentiates alkali light chains among the light fragmentation components. A non-fragmented HMM-S1 was obtained from a papain digest of myofibrils and the chromatographic analysis supplied further evidence of the separation of the two species of HMM-S1 present in rabbit white muscle myosin.     

Inhibitory effect of hydroxyurea on [3-H]leucine incorporation in human peripheral lymphocytes.

Hydroxyurea (HU), generally considered to be a specific inhibiter of DNA synthesis, has an inhibitory effect on the incorporation of TCA-precipitable [3-H]leucine in peripheral lymphocytes. This action is not secondary to the inhibition of DNA synthesis since incorporation of [3-H]leucine is unaffected when DNA synthesis is inhibited by 5-fluorodeoxyuridine (FUdR); it does not appear to be directly related to inhibition of RNA synthesis; and it is not mediated at the level of translation since HU has no effect on protein synthesis in rabbit reticulocytes. The relevance of these findings to the use of HU as a DNA inhibitor is discussed.     

Resolution of cyclic AMP stimulated protein kinase from polymerization-purified brain microtubules.

Polymerization-deploymerization purified microtubules from mouse brain contain, in addition to tubulin, several minor proteins, including protein kinase activity. The protein kinase copurifies with microtubules in constant proportion to tubulin through two, three, or four cycles of polymerization; it can be resolved from tubulin by gel filtration chromatography and has an apparent molecular weight of 280,000. Its activity is stimulated 7-fold by cyclic AMP, and resembles the soluble brain protein kinase described by Miyamoto $\text{et al.}$ (1). The microtubule preparation serves as an endogenous substrate for this protein kinase; both 6S and 30S tubulin are substrates for phosphorylation to the extent of about 0.10 ± 0.05 moles/mole.     

Sister chromatid exchanges--a sensitive assay of agents damaging human chromosomes.

Sister chromatid exchange frequencies in human lymphocyte chromosomes are greatly increased by alkylating agents, but ionizing radiation has little if any such effect. Scoring these exchanges may provide a useful technique for exploring the mechanisms of chromosome breakage and repair.     

Incorporation of methionine-[methyl-2H3] and mevalonic acid-[2-14C,(4R)-4-3H1] into Phycomyces blakesleeanus sterols

Ergosterol, episterol, 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol and 24-methylene-24,25-dihydrolanosterol, isolated from Phycomyces blakesleeanus grown in the presence of methionine-[methyl-²H₃], each contained two deuterium atoms; lanosterol, however, was unlabelled. The ¹⁴C:³H atomic ratio of the following sterols isolated from P. blakesleeanus grown in the presence of mevalonic acid-[2-¹⁴C,(4R)-4-³H₁], was: ergosterol, 5:3; episterol, 5:4; ergosta-5,7,24(28)-trien-3β-ol, 5:3; 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol, 5:4; 24-methylene-24,25-dihydrolanosterol, 6:5; lanosterol, 6:5. The significance of these results in terms of ergosterol biosynthesis is discussed.     

Biotransformation of pregnenolone - 7alpha-3H, progesterone - 7alpha-3H and dehydroepiandrosterone - 7alpha-3H by porcine fetal and maternal adrenal homogenate preparations.

The biotransformation of pregnenolone-7alpha-3H and of progesterone-7alpha-3H by porcine fetal and maternal adrenal homogenates at 56 and 112 days of pregnancy and of dehydroepiandrosterone-7alpha-3H by fetal adrenal homogenates has been investigated in vitro. Both pregnenolone-7alpha-3H and progesterone-7alpha-3H were metabolized extensively by maternal adrenal preparations, the principal radioactive metabolites isolated being cortisol, corticosterone, 11-deoxycortisol, deoxycorticosterone, 11beta-hydroxyprogesterone and androstenedione. In addition, 17alpha-hydroxyprogesterone, 20alpha-dihydroprogesterone and cortisone were formed from both substrates and 17alpha-hydroxypregnenolone and progesterone were formed from pregnenolone. Although essentially the same radioactive metabolites were isolated after incubation of fetal adrenal glands with pregnenolone-7alpha-3H or progesterone-7alpha-3H, a greater proportion of the radioactivity was associated with corticosteroids at 112 days of pregnancy than at 56 days. 11beta-Hydroxyandrostenedione and androstenedione were isolated and identified together with an unknown polar metabolite, after incubation of fetal adrenal tissue with dehydroepiandrosterone-7alpha-3H. These results are discussed in relation to feto-placental steroid biosynthesis and metabolism and the role of the fetal adrenal in the initiation of parturition in the pig.