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research-article

Differential expression of gap and pgk genes within the gap operon of Zymomonas mobilis.

Department of Microbiology and Cell Science, University of Florida, Gainesville 32611.

ABSTRACT

In Zymomonas mobilis, the genes encoding glyceraldehyde-3-phosphate dehydrogenase (GAP) and phosphoglycerate kinase (PGK) are encoded in an operon that is transcribed from tandem promoters. The promoter-proximal gap gene is expressed at six- to ninefold higher levels than the pgk gene from chromosomal genes and from multiple copies of plasmid-borne genes. Two dominant transcripts were identified. The smaller, most abundant transcript contained primarily the gap message, whereas the larger, less abundant message contained both genes. The ratio of message levels for gap and pgk was calculated to be 5:1 and is sufficient to account for the observed differences in levels of GAP and PGK. The differences in message abundance are proposed to result from either transcriptional attenuation or preferential degradation of the 3' region encoding pgk. Increases in gene dosage were accompanied by one-third the expected increase in enzymatic activity on the basis of estimates of copy number, consistent with the presence of a limiting, positive regulatory factor. However, GAP and PGK expressions were not reduced from the chromosome in recombinants that contained multiple copies of the gap operon with inactive genes.

This article has been cited by other articles:

• Charpentier, B., Bardey, V., Robas, N., Branlant, C. (1998). The EIIGlc Protein Is Involved in Glucose-Mediated Activation of Escherichia coli gapA and gapB-pgk Transcription. J. Bacteriol. 180: 6476-6483 [Abstract] [Full Text]