Antimetabolic activities of 2-fluoro-L-histidine.

2-Fluoro-L-Histidine inhibits protein synthesis in various cell cultures, as measured by ³H-leucine incorporation. This histidine analog also inhibits the cytopathogenicity of a number of RNA and DNA viruses in primary and continuous cell cultures; it blocks the transformation of normal mouse (MO) cells by murine sarcoma virus, and partially suppresses the release of murine leukemia virus by a continuously infected mouse cell line (JLSV5). In human skin fibroblasts, it reduces the interferon-inducing capacity of poly(I)·poly(C). Inhibition of cell protein synthesis may be the common cause of the various effects. 4-Fluoro-L-histidine is essentially inert in all of the test systems examined.     

Relation between slow delayed light emission and acid-base triggered luminescence in chloroplasts

Acid-base triggered luminescence in relation to slow delayed light emission (> 3 s) was studied in chloroplasts. After analyzing their time courses, the acid-base induced luminescence curve was found to return to the original curve of delayed light emission. Peaks of the acid-base triggered luminescence induced after various darkness periods following preillumination decreased parallel to the time course of delayed light emission without base treatment. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea enhanced both the delayed light emission and acid-base induced luminescence, while carbonyl cyanide m-chlorophenylhydrazone inhibited both. Several photophosphorylation uncouplers inhibited the acid-base induced luminescence without any substantial effect on the delayed light emission. It is concluded that the acid-base triggered luminescence is not caused by the reversion of electrons from remote intermediates on the reducing side of Photosystem II. The possibility of the presence of an activation pathway for the acid-base triggered luminescence which differs from that of the delayed light emission is also discussed.     

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.