Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

December 1993

Abstract

The effect of erythromycin on the 50S ribosomal subunit during cell growth has been extensively investigated. Sucrose density gradient analysis of ribosomes formed in the presence and absence of the drug revealed a 50S specific assembly defect is partially responsible for erythromycin's inhibitory effects on wild type cells. Examination of two erythromycin-resistant mutants of E. coli (N281 and N282) revealed that mutant N281 (L22 mutant) but not N282 (L4 mutant) was assembly defective in the presence of the drug, although only at much higher drug concentrations (300 ug/ml vs. 75 ug/ml for wild type cells). The altered genes from each mutant have been isolated and sequenced. The L22 mutant was found to contain a 9 bp deletion which eliminated codons 82-84, and the sequence Met-Lys-Arg from the protein. The L4 mutant had an A to G transition mutation in codon 63 resulting in a Lys to Glu change in the protein. Complementation of each mutant by their respective wild type genes resulted in an increased sensitivity to the drug in the partial diploid strains. Two other macrolide antibiotics (oleandomycin and spiramycin) were also examined but revealed no apparent assembly effect on wild type cells. The MLS antibiotics also appeared to be unable to effect assembly. However, the erythromycin derivative azithromycin showed a similar effect on assembly to that of the parent compound although clarithromycin (another erythromycin derivative) did not. These results suggest erythromycin and azithromycin effect assembly through ribosomal protein L4 and to a lesser extent through protein L22.

Document Type

Dissertation - unrestricted

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