PLASMID TRANSFER AND EXPRESSION OF THE TRANSFER (TRA) GENE-PRODUCT OFPLASMID PLJ101 ARE TEMPORALLY REGULATED DURING THE STREPTOMYCES-LIVIDANS LIFE-CYCLE

We previously have shown that a chromosomally integrated copy of the t ra gene of plasmid plJ101 under the control of the KorA repressor prot ein, which regulates transcription of tra as well as its own synthesis , can promote the conjugal transfer of both chromosomal and plasmid ge nes in Streptomyces lividans. Using an antibody generated against a fu sion protein containing the C-terminal portion of Tra, we show here th at this essential conjugation protein is present in membrane fractions of both surface-grown S. lividans, which mate readily, and of cells g rown in liquid culture, where mating has not been found, Expression of Tra during the S. lividans life cycle was temporally regulated and wa s reduced late during vegetative growth so that little or no Tra prote in was detected in cells as they began to differentiate morphologicall y and produce secondary metabolites, Comparison of the membrane concen tration of Tra protein with tra mRNA concentration during the S. livid ans life cycle indicated that the disappearance of Tra is post-transcr iptionally controlled and thus is not mediated by KorA. The results of 'interrupted mating' experiments, together with the time of appearanc e of Tra in S. lividans membranes, indicate that the intermycelial tra nsfer of plJ101 in S. lividans is complete by the onset of cellular di fferentiation.