1.E.54 The Gene Transfer Agent-release Holin (GTA-Hol) Family The gene transfer agent of Rhodobacter capsulatus (RcGTA) is a bacteriophage-like genetic element with the sole known function of horizontal gene transfer. Homologues of RcGTA genes are present in many members of the alphaproteobacteria and may serve an important role in microbial gene transfer between organisms. Transcription of RcGTA genes is induced as cultures enter the stationary phase. Westbye et al. 2013 identified the promoter of the first gene in the RcGTA structural gene cluster and showed that gene transduction frequencies depend on the growth medium. Millimolar concentrations of phosphate posttranslationally inhibit the lysis-dependent release of RcGTA from cells in both a complex medium and a defined medium. Cell lysis requires the genes rcc00555 and rcc00556, which were expressed and studied in Escherichia coli to demonstrate their functions as an endolysin and holin, respectively. Production of RcGTA is regulated by host systems, including the histidine kinase, CckA, which is required for maximal expression of rcc00555 and for maturation of RcGTA to yield gene transduction-functional particles.
References:
Westbye, A.B., M.M. Leung, S.M. Florizone, T.A. Taylor, J.A. Johnson, P.C. Fogg, and J.T. Beatty. (2013). Phosphate concentration and the putative sensor kinase protein CckA modulate cell lysis and release of the Rhodobacter capsulatus gene transfer agent. J. Bacteriol. 195: 5025-5040.
Examples:
TC#	Name	Organismal Type	Example
1.E.54.1.1	*Gene Transfer Agent (GTA) holin of 164 aas with 3 TMSs in a 1 + 2 TMS arrangement. Involved in GTA release from cells in stationary phase (Westbye et al.* 2013).**	Proteobacteria	GTA holin of Rhodobacter capsulatus

1.E.54.1.2	Putative holin of 195 aas and possibly 4 TMSs in a 1 (N-terminal) + 2 (central) +1 (C-terminal).	Proteobacteria	Putative holin of Rhodospirillum photometricum

1.E.54.1.3	Putative holin of 186 aas and 2 or 3 TMSs, one of low hydrophobicity at the N-terminus, and 2 sharper peaks for higher hydrophobicity centrally located.	Proteobacteria	Holin homologue of Saccharophagus degradans

1.E.54.1.4	Putative holin of 181 aas of the DUF3154 family.	Proteobacteria	Putative holin of Rubelimicrobium thermophilum

1.E.54.1.5	Putative holin of 177 aas and 2 - 4 TMSs.	Proteobacteria	Putative holin of Rhodospirillum photometricum

Examples:
TC#	Name	Organismal Type	Example
1.E.54.2.1	Putative holin of 134 aas and 3 TMSs, one N-terminal and two central.	Proteobacteria	Putative holin of Desulfovibrio desulfuricans

1.E.54.2.2	Putative holin of 136 aas and 2 TMSs.	Proteobacteria	Putative holin of Vibrio splendidus

1.E.54.2.3	Putative holin of 113 aas and 2 TMSs	Proteobacteria	Putative holin of Puniceispirillum marinum

1.E.54.2.4	Putative holin of 150 aas and 2 TMSs	Proteobacteria	Putative holin of Pseudoalteromonas tunicata

1.E.54.2.5	Putative holin of 196 aas and 2 or 3 TMSs.	Proteobacterial virus	*Putative holin of Salmonella* phage ViI**

1.E.54.2.6	Putative holin of 121 aas and 2 TMSs.	Proteobacteria	*Putative holin of Pelagibacter* phage HTVC011P**

Examples:
TC#	Name	Organismal Type	Example
1.E.54.4.1	Gp21 protein of 145 aas and 2-3 TMSs		*Gp21 of Cellulophaga* phage phi48:2**

1.E.54.4.2	Putative holin of 148 aas and 2 TMSs		Putative holin of Pseudoalteromonas haloplanktis

1.E.54.4.3	Uncharacterized protein of 149 aas and 2 putative TMSs		UP of Desulfatibacillum alkenivorans

1.E.54.4.4	Uncharacterized protein of 168 aas and 2 - 3 TMSs		UP of Teredinibacter turnerae

1.E.54.4.5	Uncharaterized protein of 145 aas and 2 TMSs		UP of Vibrio azureus

1.E.54.4.6	Uncharacterized protein of 132 aas and 2 TMSs		UP of Pseudoalteromonas piscicida

1.E.54.4.7	Uncharacterized protein of 87 aas and 2 TMSs		UP of Aliivibrio salmonicida (Vibrio salmonicida)

Examples:
TC#	Name	Organismal Type	Example
1.E.54.5.1	Uncharacterized protein of 137 aas and 3 TMSs		UP of Novosphingobium aromaticivorans

1.E.54.5.2	Uncharacterized protein of 144 aas and 2 - 3 TMSs		UP of Marinobacter nanhaiticus