MECHANISM OF REGULATING THE EXPRESSION OF LAMBDA-N GENE BY RIBOSOMAL-PROTEIN AT TRANSLATIONAL LEVEL

In ribosomal protein S12 mutant or L24 mutant the expression of lambda N gene was depressed at translational level. To study its mechanism t he lambda N gene region of lambda N-lacZ gene fusion was trimmed from its 5' end to 3' end with DNA exonuclease III (DNA exoIII) in order to alter the TIR (translational initiation region) and the coding region of lambda N gene. After DNA sequencing 23 species of different lambda N-lacZ fused genes were obtained. The beta-galactosidase activities o f these deletants in ribosomal protein mutant were compared with that in wild type strain. The result indicated that (i) S12 mutant could af fect 30S subunit's binding to the TIR of lambda N gene messenger and c ause the difficulty in forming 30S initiation complex and then decreas e the efficiency of translational initiation; (ii) in S12 mutant the c oding region of lambda N gene also affected the expression of lambda N gene; (iii) in L24 mutant the inhibition of lambda N gene expression was not related to translational initiation and the 5' end of the codi ng region of lambda N gene, but related to the 3' end of lambda N gene .