This family contains a number of bacterial Syd proteins approximately 180 residues long. It has been suggested that Syd is loosely associated with the cytoplasmic surface of the cytoplasmic membrane, and that interaction with SecY may be involved in this membrane association [1]. Operon analysis showed that Syd protein may function as immunity protein in bacterial toxin systems [2].

1: Product of a new gene, syd, functionally interacts with SecY when overproduced in Escherichia coli. Shimoike T, Taura T, Kihara A, Yoshihisa T, Akiyama Y, Cannon K, Ito K; J Biol Chem 1995;270:5519-5526. PMID:7890670

2: A novel immunity system for bacterial nucleic acid degrading toxins and its recruitment in various eukaryotic and DNA viral systems. Zhang D, Iyer LM, Aravind L; Nucleic Acids Res. 2011;39:4532-4552. PMID:21306995