Mutants resistant to 3-aminobenzamide, a known inhibitor of ADP-ribosyltransferase, were obtained from IFO 13189, a streptomycin-producing strain. One (strain no. 4), which had significantly reduced ADP-ribosyltransferase activity, was analysed in detail. Mutant 4 displayed a conditional phenotype with respect to cultivation temperature. At 30 °C, it exhibited severely reduced ability to produce aerial mycelium (on solid medium) and submerged spores and streptomycin (in liquid culture), but this ability was fully restored at 25 °C. The mutant produced A-factor normally, regardless of cultivation temperature, and exhibited normal ability to accumulate ppGpp intracellularly. SDS-PAGE analyses of cellular proteins labelled by [P]NAD revealed that an ADP-ribosylated protein with a molecular size of 44 kDa, which appeared in sporulating cultures of the parent strain, was missing from the mutant grown at the non-permissive temperature (30 °C). Genetic analysis showed that the mutation conferring resistance to 3-aminobenzamide was tightly linked to the altered phenotype. Failure to ADP-ribosylate certain cellular protein(s), presumably due to the mutation, may be responsible for impaired differentiation in this mutant.


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