In addition to Sam68, two related Sam68 family members, Sam68 Like Mammalian (SLM)- 1 and SLM-2 (also known as T-Star or Etoile), have been shown to localize in SNBs (Chen et al., 1999) . Other proteins found to localise to SNBs include: the alternative splicing factor YT521-B (Hartmann et al., 1999); the soluble tyrosine kinase BRK/SIK (Breast tumor Kinase/ Src-related Intestinal Kinase) (Derry et al., 2000); and HAP (hnRNP A1 associated protein) (Denegri et al., 2001). Interestingly, the SNBs are able to recruit some splicing factors of the SR family upon stress induction (Denegri et al., 2001).

SNB function

The function of SNBs is unknown. SNBs have only been found in immortalized and primary cell lines. Thus, their predominant presence in highly transformed and poorly differentiated cell lines, such as HeLa and BT-20, suggest that SNBs may be a marker for these types of cancer cells. Many SLM proteins share SH2 and SH3 domains, suggesting this family of proteins may serve as adaptor proteins for cellular protein kinases. In addition, their ability to bind RNA and the presence of splicing factors in SNBs suggest that they may play a role in coupling signal transduction pathways to pre-mRNA processing. Further support for a role in RNA metabolism comes from the recent evidence that rat SLM-2 can interact via two-hybrid with several splicing factors (SRp30c, YT521-B and SAF B) and can regulate the alternative splicing of a CD44 mini gene (Stoss et al., 2001).