Transferrin-dependent expression of TbpA by Histophilus ovis involves a poly G tract within tbpA.
A poly G tract in tbpA of Histophilus ovis strain 3384Y was suspected of being responsible for the transferrin (Tf)-dependent expression of TbpA. The region encompassing the poly G tract was amplified using DNA from H. ovis strains 9L and 3384Y grown under iron-replete conditions and under iron-restricted conditions in the presence of bovine Tf. Sequence analysis of the amplification products revealed that regardless of the growth conditions, the poly G tract in strain 9L contained eight Gs, a situation that maintains the correct reading frame of the gene. Similarly, the poly G tract in strain 3384Y contained eight Gs when the organisms were grown under iron-restricted conditions in the presence of bovine Tf but when grown under iron-replete conditions, the poly G tract contained nine Gs resulting in a frame shift and the introduction of a premature stop codon. It is concluded that the Tf-dependent expression of TbpA in H. ovis strain 3384Y is due to a form of phase variation.
Ekins
Andrew
A
Microbiology Unit, Department of Natural Resource Sciences, Macdonald Campus, McGill University, 21111 Lakeshore Road, Ste. Anne de Bellevue, QC, Canada H9X 3V9.
Niven
Donald F
DF
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D018388:Codon, Terminator; D004269:DNA, Bacterial / Q000235:genetics*; D016368:Frameshift Mutation; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics*; D005798:Genes, Bacterial; D007501:Iron / Q000378:metabolism; D008969:Molecular Sequence Data; D015661:Pasteurellaceae / Q000235:genetics*; D011068:Poly G / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D014168:Transferrin / Q000494:pharmacology*; D033881:Transferrin-Binding Protein A / Q000096:biosynthesis* / Q000235:genetics
D018388:Codon, Terminator; D004269:DNA, Bacterial; D014168:Transferrin; D033881:Transferrin-Binding Protein A; D011068:Poly G; D007501:Iron