The in vivo Expression of Streptomyces rimosus tRNA Genes

Sonja Durajlija Žinić*, Miroslav Plohl and Vera Gamulin

Department of Molecular Genetics, »Ruđer Bošković« Institute, Bijenička c. 54, HR-10000 Zagreb, Croatia

Article history:
Received February 17, 2000
Accepted April 7, 2000

Key words:
Streptomyces rimosus, expression, promoter, tRNA genes

Summary:
The expression of seven tRNA genes from Streptomyces rimosus, cloned on bifunctional plasmids, has been studied in a homologous (S. rimosus) and a heterologous (Escherichia coli) system. Analyzed genes included cluster of genes containing two tRNA^Gln and three tRNA^Glu genes and two independent tRNA^fMet genes. Northern hybridization analysis showed that all tRNA genes on plasmids are transcribed and processed in the homologous system. In the E. coli system only the cluster of Gln-Glu tRNA genes is properly expressed. From the deletion experiments it can be concluded that in both species all five genes in the cluster are cotranscribed from the same promoter, located 140–65 bp upstream from the first gene. A sequence TTGGAC-17-TAATGT resembling to Streptomyces-E. coli (SEP) promoter is located in this region. Similar sequence TTGCGC-18-TAGACT was also found 13 bp upstream from the tRNA^fMet1 gene. However, this gene is not properly expressed in E. coli. Putative promoter of the tRNA^fMet2 gene could not be easily identified by sequence homology in relation to two other presumptive promoters of tRNA genes. Streptomycetes promoters show huge sequence heterogeneity and two tRNAfMet genes obviously have very different promoters. 

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