Two regions in human DNA polymerase β mRNA suppress translation inEscherichia coli

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Abstract
Although human DNA polymerase β (DNA polβ) shows 96% Identity with rat DNA pol at the amino acid level, it is weakly expressed in Escherlchla (E.) coli relative to the rat enzyme. The mechanism of this suppression was investigated. Pulse-chase protein labeling and steady state mRNA analysis showed that mature human DNA polβ protein is relatively stable in E.coli and the levels of human and rat DNA polβ mRNA were comparable indicating that the human DNA pol β expression is suppressed at the translational level. By systematic expression analysis of a number of chimeric genes composed of human and rat cDNAs, two strong translational suppression regions were mapped in the human DNA polβ mRNA; one was named TSR-1, corresponding to CGG encoding arginine (arg) at postition 4 and the other, termed TSR-2, is located between codons 153 and 199. SInce substitution of the rat Arg-4 codon with synonymous codons showed strong effects upon the expression level, we propose that the arg codon at the N-terminal cording region plays a role in modulating expression.