Alteration of regulation of arginine biosynthesis in Escherichia coli W by mutation to rifampin resistance.

The synthesis of acetylornithine delta-transaminase is induced by arginine and by rifampin in an arginine-inducible mutant of Escherichia coli W. A mutant of the arginine-inducible strain was isolated which is resistant to rifampin. The mutation which has brought about rifampin resistance has altered RNA polymerase and has simultaneously altered the regulation of arginine biosynthesis. Three of the enzymes of arginine biosynthesis, acetylornithinase, ornithine transcarbamylase, and argininosuccinase, show a greater rate of derepression and a 2--12-fold higher level of enzyme activity in the rifampin-resistant mutant than in the parent arginine-inducible strain. Acetylornithine delta-transaminase is no longer inducible by rifampin alone, and the level of inducibility by arginine plus rifampin has been reduced by 70%. The results indicate that RNA polymerase is involved in regulation of arginine biosynthesis in E. coli W.

Transformation of 25-Hydroxycholesterol by Rhizoctonia muneratii.

Rhizoctonia muneratii ATCC 13247 was capable of catalyzing the conversion of 25-hydroxycholesterol to the 3-oxo-4-ene. Hydroxylation at the 6alpha and 6beta positions with the concomitant 3-oxo-4-ene transformation was also observed. The addition of Triton X-100 to the growth medium immediately before steroid addition selectively prevented the appearance of the respective 6alpha-hydroxylated products. The observed conversions were indicative of the utility of microbial transformations in preparing hydroxylated steroids which can be useful for further synthetic modification or for study as pharmacological agents.