Transfer genes or tra genes (also transfer operons or tra operons), are some genes necessary for non-sexual transfer of genetic material in both

gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bac ...

and

gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

. The tra locus includes the

pilin Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. These structures can be used for the exchange of genetic material, or as a cell adhesion mechanism. Although not all bacteria have pili or fimbriae, bact ...

gene and regulatory genes, which together form pili on the cell surface, polymeric proteins that can attach themselves to the surface of F-bacteria and initiate the conjugation. The existence of the tra region of a

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; ho ...

genome was first discovered in 1979 by David H. Figurski and Donald R. Helinski In the course of their work, Figurski and Helinski also discovered a second key fact about the tra region – that it can act in ''

trans Trans- is a Latin prefix meaning "across", "beyond", or "on the other side of". Used alone, trans may refer to: Arts, entertainment, and media * Trans (festival), a former festival in Belfast, Northern Ireland, United Kingdom * ''Trans'' (film ...

'' to the mobilization marker which it affects. This finding suggested that there were two basic aspects necessary for a plasmid to move from one cell to another: # An

origin of transfer An origin of transfer (''oriT'') is a short sequence ranging from 40-500 base pairs in length that is necessary for the transfer of DNA from a gram-negative bacterial donor to recipient during bacterial conjugation. The transfer of DNA is a critical ...

– A plasmid with no origin of transfer is non-mobilizable. # The transfer genes – Though a functioning set of tra genes is necessary for plasmid transfer, they may be located in a variety of places including the plasmid in question, another plasmid in the same host cell, or even in the bacterial genome. The tra genes encode proteins which are useful for the propagation of the plasmid from the host cell to a compatible donor cell or maintenance of the plasmid. Not all transfer operons are the same. Some genes are only found in a few species or a single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...

of bacteria while others (such as ''traL'') are found in very similar forms in many bacterial species. Many of the transfer systems are incompatible. For example, ''oriT'' and ''bom'' are two origins of transfer which interact with different sets of transfer genes. A plasmid with a mob site (like many found in ''

Rhodococcus ''Rhodococcus'' is a genus of aerobic, nonsporulating, nonmotile Gram-positive bacteria closely related to ''Mycobacterium'' and '' Corynebacterium''. While a few species are pathogenic, most are benign, and have been found to thrive in a broad ...

'' species) cannot be transferred via transfer genes which normally interact with the oriT site (which is common in ''E. coli'') Each of the individual genes in the tra

operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...

codes for a different protein product. These products may perform a number of tasks including interaction with one another to perform mating pair functions and regulation of different regions of the tra operon itself, or conjugative DNA metabolism and surface exclusion. Also, note that some proteins perform multiple functions or are associated closely with proteins which have non-similar functions.

References

{{DEFAULTSORT:Transfer Gene Genes