This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ducote, M. J. Articles by Pettis, G. S. Search for Related Content PubMed PubMed Citation Articles by Ducote, M. J. Articles by Pettis, G. S.

 Previous Article  |  Next Article 

Journal of Bacteriology, July 2003, p. 3780-3787, Vol. 185, No. 13
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.13.3780-3787.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Common and Distinguishing Regulatory and Expression Characteristics of the Highly Related KorB Proteins of Streptomycete Plasmids pIJ101 and pSB24.2

Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803

Received 26 December 2002/ Accepted 15 April 2003

The conjugative plasmid pIJ101 of the spore-forming bacterium Streptomyces lividans contains a regulatory gene, korB, whose product is required to repress potentially lethal expression of the pIJ101 kilB gene. The KorB protein also autoregulates korB gene expression and may be involved in control of pIJ101 copy number. KorB (pIJ101) is expressed as a 10-kDa protein in S. lividans that is immediately processed to a mature 6-kDa repressor molecule. The conjugative Streptomyces cyanogenus plasmid pSB24.1 is deleted upon entry into S. lividans to form pSB24.2, a nonconjugative derivative that contains a korB gene nearly identical to that of pIJ101. Previous evidence that korB of pSB24.2 is capable of overriding pIJ101 kilB-associated lethality supported the notion that pIJ101 and pSB24.2 encode highly related, perhaps even identical conjugation systems. Here we show that KorB (pIJ101) and KorB (pSB24.2) repress transcription from the pIJ101 kilB promoter equally well, although differences exist with respect to their interactions with kilB promoter sequences. Despite high sequence and functional similarities, KorB (pSB24.2) was found to exist as multiple stable forms ranging in size from 10 to 6 kDa both in S. lividans and S. cyanogenus. Immediate processing of KorB (pIJ101) exclusively to the 6-kDa repressor form meanwhile was conserved between the two species. A feature common to both proteins was a marked increase in expression or accumulation upon sporulation, an occurrence that may indicate a particular need for increased quantities of this regulatory protein upon spore germination and resumption of active growth of plasmid-containing cells.