Enhanced transformability with heterospecific deoxyribonucleic acid in a Streptococcus sanguis mutant impaired in ribonucleic acid polymerase activity

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Abstract
Nitrosoguanidine was used to induce a mutation in S. sanguis conferring inability to grow and synthesize RNA at 42.degree. C, the optimal temperature for growth and RNA synthesis in the parental strain. The mutation (ts) is transferable via transforming DNA and is replaceable by its wild-type allele with fairly high efficiency in transformation reactions. The ts mutation is unlinked to the mutation sites conferring resistance to rifampin (rifr) and streptolydigin (stgr), known to affect the .beta. subunit of DNA-dependent RNA polymerase. Extracts from strains carrying the ts mutation are more sensitive to elevated temperatures than are parental extracts when assayed for DNA-dependent RNA polymerase. That the mutation causes a temperature-sensitive defect in some component of this enzyme (other than .beta.) is supported by the finding that the polymerase activity of a heat-inactivated ts stgr extract cannot be increased by addition of an unheated ts stgs extract which is itself inactivated by streptolydigin. S. sanguis recipients carrying the ts mutation are highly transformable with heterospecific [S. pneumoniae] DNA, especially at the restrictive temperature.