Molecular Comparisons of Colicin Ia and Colicin Ib (Dna Sequence, Secondary Structure, Immunity Genes)
Mankovich, John Alan
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https://hdl.handle.net/2142/71173
Description
Title
Molecular Comparisons of Colicin Ia and Colicin Ib (Dna Sequence, Secondary Structure, Immunity Genes)
Author(s)
Mankovich, John Alan
Issue Date
1985
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Abstract
Colicin Ia and colicin Ib have three distinct functional characteristics, receptor specificity, mode of action and immunity recognition. Both colicins bind to the same receptor and kill sensitive Escherichia coli cells by depolarizing the cell membrane. Sensitive cells carrying the colicin Ib structural and immunity genes are immune to colicin Ib but sensitive to the killing effect of colicin Ia and vice versa.
Analysis of the immunity specificities of hybrid proteins and the direction of transcription of the colicin Ib structural gene have led to the conclusion that the immunity recognition domain of the colicin molecule resides in the COOH-terminal half of the molecule. Hybrid proteins were constructed by ligating cloned fragments of the colicin Ib gene with fragments of the colicin Ia gene and cloning them into E. coli. Direction of transcription of the colicin Ib gene was determined by cloning the intact gene into the E. coli expression vector pKC101 which allows expression of inserted genes to be under the control of the left promotor (p(,L)) of bacteriophage Lambda.
Both colicin Ia and Ib structural and immunity gene DNA sequences have been determined and a comparison of the two sequences reveal a great deal of sequence conservation. The colicin structural genes are nearly identical in what corresponds to the amino-terminal two-thirds of the molecules. The region of the molecules containing the immunity recognition domains is also the area of least homology. The DNA sequences corresponding to the immunity genes have no homology, however, the hydrophilicity profiles of the predicted proteins are very similar. Codon usage throughout the coding regions for the colicin and immunity genes does not reflect the bias of that seen in known E. coli genes. The codon choice of the colicins and their immunity genes is similar to that seen in the other membrane active colicins.
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