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SUMMARYNitrate reductase (NR) activity, induced by germination in KNO3 showed a strong rhythmicity during the early stages of germination of wheat embryos. Peaks of activity occurred approximateiy every 12 h. Tbere was no relationship hetween the amounts of nitrate in tbe embryos and enzyme activity. Tbe fluctuations in enzyme activity did not appear to be due to reversible inactivation of the enzyme. Some evidence suggests that tbe fluctuations in enzyme activity may result from a more rapid degradation of enzyme during the decreasing phase of the rhythm.

CNBr treatment of calf thymus [methyl-14C]histone H4, methylated in vitro with S-adenosyl-L-[methyl-14C]methionine by a highly histone-specific wheat germ protein methylase I (S-adenosyl-L-methionine:protein-L-arginine N-methyltransferase, EC 2.1.1.23), produced two peptide fragments corresponding to residues 1-83 and 84-102, with the former being radioactive. Two-dimensional peptide mapping of the chymotryptic and tryptic digest of [methyl-14C]histone H4 and analysis of the chymotryptic digest on HPLC have shown that only a single peptide is radiolabeled. In order to define the exact site of methylation (arginine residue), the radioactive peptide from the chymotryptic digest of [methyl-14C]histone H4 was further purified on HPLC by linear and then isocratic elution. The purified chymotryptic peptide was then digested with trypsin and purified on HPLC, and its amino acid composition was determined on HPLC. These results indicate that the peptide corresponding to residues 24-35 of histone H4 is radiolabeled. Since this peptide contains a single arginine residue at position 35, we have concluded that the enzyme is specific not only to the protein substrate but also to the methylation site.

Sodium arsenite was found to stimulate an SV40-transformed BALB/c cell line (SVT2) to synthesize a 31-kDa protein within 2.5 h. This SVT2 protein was purified to homogeneity. It is a nuclear protein which appears to be associated with membranes because it is not extractable from nuclear membrane preparations by 2 M salt. It is highly hydrophobic, eluting from a reverse-phase HPLC column at a similar acetonitrile concentration as a previously described 31-kDa BALB/c-3T3 cell nuclear protein. However, digestion of highly purified BALB/c-3T3 and SVT2 cell proteins with V8 protease revealed nonidentical fragmentation patterns. Moreover, amino acid analysis of the two proteins was also dissimilar, indicating different primary structures. Thus, these two nuclear membrane associated proteins appear to be distinct species.