A TRANSCRIPTION TERMINATOR IN THE THYMIDYLATE SYNTHASE (THYA) STRUCTURAL GENE OF ESCHERICHIA-COLI AND CONSTRUCTION OF A VIABLE THYA-KMR DELETION

A transcription terminator has been identified within the coding sequence of the Escherichia coli thyA gene. Fusion of a relevant segment of the thyA structural gene to galK sequences showed that the terminator functions in vivo. Primer extension and Northern hybridization (RNA blot) analysis of the thyA RNA suggested that the terminator acts as the transcription stop signal for an upstream gene and for thyA-specific transcripts. Results from antitermination studies utilizing a lambda-p(L)-thyA fusion also offer evidence that the terminator is capable of attenuating thyA expression by reducing the amount of full-length thyA transcripts. This gene arrangement suggested that previous unsuccessful attempts to create a chromosomal thyA deletion into the nonoverlapping portion of the cloned thyA gene and inserting a gene encoding kanamycin resistance produced a (DELTA-ThyA::Km(r) that was easily transferred to the chromosome of recD host by marker replacement. This DELTA-thyA::Km(r) allele provides a useful and readily transducible chromosomal marker.