Biochemical correlates of cardiac hypertrophy. II. Increased rate of RNA synthesis in experimental cardiac hypertrophy in the rat

Cardiac hypertrophy was produced in rats by banding the ascending aorta. Increases in heart weight and RNA content occurred within 48 hours, indicating that hypertrophy develops rapidly. The total RNA content and the specific radioactivity of RNA labeled with 3 H-uridine were determined. The rate of RNA synthesis was estimated from these data and from the specific radioactivity of the myocardial uridine nucleotide pool. The rate of RNA synthesis in hearts of banded animals averaged four times greater than controls on the second postoperative day and about two to three times greater on the fourth to fifth postoperative days. An expansion of the myocardial uridine nucleotide pool was observed in banded rats, but the size of the myocardial adenosine nucleotide pool was not changed. No changesin base composition of 28S, 18S, or 4S RNA were observed following cardiac hypertrophy.

Reaction of nitrosoguanidine (N-methyl-N'-nitro-N-nitrosoguanidine) with tobacco mosaic virus and its RNA

"Nitrosoguanidine" (N-methyl-N'-nitro-N-nitrosoguanidine) acts on polynucleotides in neutral aqueous solution, methylating guanine in the 7-position, and, to a much lesser extent, adenine. In 67 percent dimethylformamide the effect on the purines decreased, and what seems to be 3-methyl-cytosine appeared. In formamide solution no base changes were detected. Nitrosoguanidine had little mutagenic effect on tobacco mosaic virus RNA in water; it had greater effect in dimethylformamide, and even greater in formamide; it was a strong mutagen only when it acted on intact tobacco mosaic virus particles. Thus, neither the methylation of guanine nor the cytosine modification represents the main mutagenic event.

Mutant of Bacterium paracoli 5099 with an altered DNA: identification as a Flavobacterium

A difference in the base composition of the DNA of Bacterium paracoli 5099 and of a "mutant" (No. 1975) derived from it was found. This is in accordance with the finding of others. However, biochemical tests revealed that the "mutant" was a Flavobacterium, whereas the parent strain belonged to a species of Escherichia. The base composition of the DNA of the "mutant" is similar to that reported for the DNA of Flavobacterium.