GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

PMID:38236051

Bacteriophage P22 SieA-mediated superinfection exclusion.

A single chromosomal copy of P22 sieA is sufficient to lower P22 plaque formation by at least seven orders of magnitude, with no effect on host growth.

"Thus, the sieA gene in one copy per Salmonella genome is sufficient to mediate robust superinfection exclusion."
SieA blocks DNA injection itself: infection of a sieA+ strain causes almost no K+ efflux, whereas the isogenic sieA- strain releases nearly all cellular K+.

"Figure 2A shows that P22 causes very little, if any, K+ release from the sieA+ strain, while nearly all of the cellular K+ is released from the isogenic sieA– strain, suggesting that DNA injection per se is blocked by SieA."
FLAG-tagged, exclusion-competent SieA fractionates with the inner membrane and is absent from the outer membrane.

"We conclude that SieA is an exclusively inner membrane protein."
Escape from SieA requires amino acid changes in the C-terminal regions of the ejection proteins gp16 and gp20, implicating the DNA delivery conduit as the target.

"Since amino acid changes in E-proteins gp16 and gp20 confer escape from SieA exclusion, we conclude that SieA very likely blocks P22 DNA injection by interfering with the functions of these two proteins and that the mutations avoid this interference."
Exclusion is specific for P22-like phages; unrelated tailed phages, including the short-tailed phage SP6, plate equally on sieA+ and sieA- hosts.

"Since SP6 is not affected, the P22 SieA protein does not exclude all short-tailed phages and appears to be specific for P22-like phages."

PMID:4610992

Superinfection exclusion by P22 prophage in lysogens of Salmonella typhimurium. III. Failure of superinfecting phage DNA to enter sieA+ lysogens.

In sieA+ lysogens the DNA of superinfecting P22 fails to enter the cell, placing the sieA block at DNA entry rather than at adsorption.

"Failure of superinfecting phage DNA to enter sieA+ lysogens."

PMID:7768804

The superinfection exclusion gene (sieA) of bacteriophage P22: identification and overexpression of the gene and localization of the gene product.

The sieA gene encodes a predicted multi-pass membrane protein with three membrane-spanning hydrophobic regions, inferred to lie in the inner membrane of the lysogenic Salmonella cell.

"According to three hydrophobic regions, all of which are long enough to span the membrane, the product of sieA should be a protein of the inner membrane of a P22-lysogenic cell of Salmonella typhimurium."
Overproduced SieA is recovered from the membrane fraction, without separation of inner from outer membrane.

"The SieA protein was moderately overproduced from an expression vector in cultures of Escherichia coli and could be recovered from the membrane fraction."