Survival Of Motor Neuron Protein Interacting Protein 1 (SIP1)

SIP1 is expressed as a 1.3-kb transcript that encodes a 279-amino acid protein with a calculated molecular mass of 32 kD. Xenopus SIP1 is 90% identical to human SIP1 at the amino acid level. In addition, human SIP1 has significant identity with S. cerevisiae Brr1, which has been shown to be involved in snRNP biogenesis. Liu et al. (1997) demonstrated that SMN and SIP1 interact tightly in vivo and in vitro and colocalize in gems in the nucleus as well as in the cytoplasm. Immunopurification of the 300-kD SMN-SIP1 complex showed that it contains, besides SMN and SIP1, spliceosomal snRNP core proteins. SMN interacted with several snRNP Sm core proteins and contains 2 distinct binding sites, one for SIP1 and one for the Sm proteins.