No abstract

The chloroplast DNA of wild-type Chlamydomonas reinhardtii was isolated in a CsCl density gradient as a single, homogeneous density class with a mean density of 1.695 g/cm(3). Irrespective of sheared size, denatured chloroplast DNA renatured as a single homogeneous species. Compositional heterogeneity, presumably intramolecular, was revealed by the absorbance-temperature profile. The complement of unique nucleotide sequences of the chloroplast DNA, as determined by the rate of renaturation, was 1.94 x 10(8) daltons. This kinetic complexity is 26-fold less than the DNA content of a single gamete chloroplast, and 52-fold less than the chloroplast of a vegetative cell, which indicates that the chloroplast of C. reinhardtii possesses at least 26 copies of a unique nucleotide sequence.

The methylation of ribosomal and transfer ribonucleic acid (RNA) synthesized after the induction of a hydrolase for S-adenosylmethionine by phage T3 infection is reducible to 50% of the methylation of RNA in uninfected cells. Hypomethylated ribosomal RNA is found in 70S particles that dissociate in 100 ,lM Mg++ to yield only 30S and 50S subunits. By this criterion, the omitted methyl groups apparently are not required for ribosomal maturation or stability. The rate of production of alkaline phosphatase in a phosphatase amber mutant was examined after phage infection in the presence and in the absence of streptomycin to determine the effect on the translation process consequent to S-adenosyl-L-methionine (SAM) hydrolase induction. Significant increases in the rates of phosphatase production were found when ultraviolet-inactivated T3 or streptomycin was added. The effects were cumulative when the cells were treated with both bacteriophage and the drug. Ultraviolet-inactivated T7, a phage closely related to T3 but which does not produce the SAM hydrolase, did not enhance the rate of alkaline phosphatase production. We suggest that the production of SAM hydrolase affects the stability of the translation process by the observed hypomethylation or by mechanisms concerning polyamine metabolism. grown with limiting amounts of methionine, the methylation of RNA is preferentially spared and 398