| During the course of this dissertation, two overlapping DNA fragments were cloned from Streptomyces coelicolor that accelerated aerial mycelium formation in the closely related species, S. lividans. 8,885 bp of DNA was subjected to genetic and sequence analysis and found to contain a cluster of five genes which were designated, ramC, ramA, ramB, ramR and ramX. ramC was shown to be required for aerial mycelium formation by mutation of its chromosomal copy in S. lividans. ramC could encode a protein similar to a group of bacterial serine/threonine kinases. ramA and ramB appear to encode similar proteins which are closely related to a class of bacterial ATP-dependent membrane translocators called bacterial ABC (ATP-Binding Cassette) exporters. ramB has been demonstrated to be necessary for aerial mycelium formation by the disruption of its chromosomal gene copy in S. lividans. ramR, which also has been proved to require for aerial mycelium formation by the disruption of its chromosomal copy, probably encodes a protein similar to a subclass of response regulators of prokaryotic two component regulatory systems. The putative ramX protein has no significant similarity to any protein sequences in the Entrez:sequence database (release 14, 1995). The study also analyzed the activities of the ram gene promoters during S. coelicolor development and examined the effects of developmental mutations on the ram gene promoters in both S. coelicolor and lividans using a tyrosinase-based reporter vector. ramC, ramA and ramB could be in the same operon, and ramA and ramB are probably translationally coupled. The ramCAB promoter could be subjected to developmental regulation and was found not to be expressed in the ramR mutant, or in bldB or bldI mutant strains. The ramR product may be directly involved in transcription of ramCAB. The ramR promoter was not found to be regulated through during S. coelicolor development, although its activity was much lower in some bld mutants than in wildtype. |
