Transfer gene
Encyclopedia
Transfer operon, commonly called tra operon, or tra genes, are some of the genes necessary for non-sexual transfer of genetic material in both gram-positive
and gram-negative
bacteria. The tra locus includes the pilin 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
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
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:
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
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 mob are two origins of transfer which interact with different sets of transfer genes. A plasmid with a mob site (like many found in Rhodococcus
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
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.
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
and gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacteria. The tra locus includes the pilin 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
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
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
Trans is a Latin noun or prefix, meaning "across", "beyond" or "on the opposite side".Trans may refer to:- Science and technology :* Cis-trans isomerism, in chemistry, a form of stereoisomerism...
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 transferOrigin of transferAn origin of transfer is a short sequence of DNA that is necessary for transfer of a bacterial plasmid from a bacterial host to recipient during bacterial conjugation. The oriT is cis-acting - it is found on the same plasmid that is being transferred, and is transferred along with the plasmid...
– The oriT (or mob) site must be located on the plasmid itself to allow recognition of the plasmid and initiation of transfer. 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
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
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 mob 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
Rhodococcus is a genus of aerobic, nonsporulating, nonmotile Gram-positive bacteria closely related to Mycobacteria and Corynebacteria. While a few species are pathogenic, most are benign and have been found to thrive in a broad range of environments, including soil, water, and eukaryotic cells...
species) cannot be transferred via transfer genes which normally interact with the oriT site (which is common in E. coli)
| The roles of some tra-gene encoded proteins: | |
| Pili Assembly and Production | traA, traB, traE, traC, traF, traG, traH, traK, traL, traQ, traU, traV, traW, |
| Inner Membrane Proteins | traB, traE, traG, traL, traP |
| Periplasmic Proteins | traC, traF, traH traK, traU, traW |
| DNA transfer | traC, traD, traI, traM, traY |
| Surface Exclusion Proteins | traS, traT |
| Mating Pair Stabilization | traN, traG |
Each of the individual genes in the tra operon
Operon
In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...
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.