Signal Recognition Particle 9kDa (SRP9)

Signal-recognition-particle assembly has a crucial role in targeting secretory proteins to the rough endoplasmic reticulum membrane. SRP9 together with SRP14 and the Alu portion of the SRP RNA, constitutes the elongation arrest domain of SRP. The complex of SRP9 and SRP14 is required for SRP RNA binding.SRP is a ribonucleoprotein machine that controls the translation and intracellular sorting of membrane and secreted proteins. The SRP contains a core RNA subunit with which six proteins are assembled. Some Alu transcripts are converted by 3-prime processing to a poly(A)-, monomeric species known as small cytoplasmic (sc) Alu RNA. The 'Alu domain' of SRP consists of 2 proteins referred to as SRP9 (9 kD) and SRP14 and the Alu-homologous region of 7SL RNA. Information on SRP9 and SRP14 has been obtained from the study of the genes in the dog and mouse, respectively. The human and mouse SRP14 proteins are about 90% identical (Chang et al., 1994). Hsu et al. (1995) cloned the human SRP9 cDNA and showed that the predicted protein was approximately 96% similar to its canine homolog.