Martine Chartier

Complete nucleotide sequence of the structural gene for colicin A, a gene translated at non-uniform rate*

The complete nucleotide sequence of the structural gene for colicin A has been established. This sequence consists of 1776 base-pairs. According to the predicted amino acid sequence, the colicin A polypeptide chain comprises 592 amino acids and has a molecular weight of 62,989. The amino-terminal part is rich in proline and glycine and accordingly secondary structure prediction indicates that this region (1 to 185) is beta-structured. The rest of the molecule (residues 186 to 592) is very rich in alpha-helix. An uncharged amino acid sequence of 48 residues is located in the C-terminal part of the molecule, which is involved in the membrane depolarization caused by colicin A. A similar region has been found in colicin E1, which has the same mode of action as colicin A. Three peptides of these bacteriocins were found to be homologous, but a comparison of the bacteriocin genes did not reveal any significant homology out of the corresponding regions. The codon usage of both genes, however, exhibits some similarity and is quite different from that of genes coding for highly or weakly expressed proteins of Escherichia coli.

Lysis protein encoded by plasmid ColA-CA31

SummaryA gene, cal, coding for a polypeptide needed for the release of colicin A from Escherichia coli cells has been identified by transposon insertion. The cal gene was located on the ColA plasmid map adjacent to cai, the gene coding for colicin A immunity protein, and therefore 592 bases downstream from caa, the structural gene for colicin A. Transcription of cal is in the same direction as caa, that is in the opposite direction to cai. Its sequence has been determined and the predicted amino acid composition features a basic N-terminal end followed by a serie of hydrophobic residues similar to the signal sequence in precursors of exported proteins. The C-terminal part also contains a core of hydrophobic residues. The overall amino acid sequence of the cal protein is homologous to that of lytic proteins encoded by the related plasmids pColE1, and pCloDF13. The cal protein has been identified on urea-SDS-polyacrylamide gels by selective labelling with various radioactive amino acids and its synthesis is co-induced with that of colicin A. The cal protein undergoes slow processing with loss of the N-terminal “signal” region and the mature form is released into the medium together with colicin A.

The complete nucleotide sequence of the colicinogenic plasmid ColA. High extent of homology with ColE1

SummaryThe complete nucleotide sequence of the colicinogenic plasmid ColA has been determined. The plasmid DNA consists of 6720 bp (molecular weight 4.48×106). Fifteen putative biological functions have been identified using the functional map previously determined. These include 11 genes and 3 DNA sites. Nine genes encode proteins of which 3 have been fully characterized. The replication region of ColA coding for RNAI and RNAII is highly homologous to that of ColE1 andClo DF13. The same holds true for the site-specific recombination region containing palindromic symmetry and involved in stable maintenance of the plasmids. A high percentage of homology has been detected for putative mobility proteins encoded by ColA and ColE1. The exclusion proteins are also highly homologous.