BIOSYNTHESIS OF RNA-POLYMERASE IN ESCHERICHIA-COLI .5. DEFECTS OF SUBUNIT ASSEMBLY IN A TEMPERATURE-SENSITIVE BETA-SUBUNIT MUTANT

[摘要] Defects in DNA-dependent RNA polymerase [EC 2.7.7.6] subunit assembly were analyzed in a temperature-sensitive .beta. subunit mutant (A2R7) of E. coli. At the permissive temperature (30.degree. C) considerable amounts of the assembly intermediate (.alpha.2.beta. complex) and premature core (.alpha.2.beta..beta.'' complex) were accumulated and were ultimately integrated into the complete enzyme structure without noticeable degradation. This mutant also accumulated a large amount of free .alpha. subunit when the culture temperature was raised to 42.degree. C, while at the same time rapid and preferential degradation was observed for .beta. and .beta.'' subunits. The mutant is apparently defective in the formation and activation of premature core at 30.degree. or 42.degree. C. The association of .alpha. subunit with the altered .beta. subunit is blocked at the non-permissive temperature (42.degree. C).