Stimulates the activity of serine palmitoyltransferase (SPT). The composition of the serine palmitoyltransferase (SPT) complex determines the substrate preference, complexes with this subunit showing a clear preference for longer acyl-CoAs. The SPTLC1-SPTLC2-SPTSSB complex shows a strong preference for C18-CoA substrate, while the SPTLC1-SPTLC3-SPTSSB isozyme displays an ability to use a broader range of acyl-CoAs, without apparent preference. Lipid metabolism; sphingolipid metabolism. Interacts with SPTLC1; the interaction is direct. Component of the serine palmitoyltransferase (SPT) complex, composed of SPTLC1, either SPTLC2 or SPTLC3, and either SPTSSA or SPTSSB (By similarity). Expression is strong in hypogonadal (hpg) mouse prostate, weak in mature castrated mouse prostate and absent in normal intact or androgen-replaced hpg mouse prostates. While expression is androgen independent in the hpg mouse prostate, it appears to be androgen-dependent in the kidney and brain of normal intact mouse suggesting tissue specific regulation by androgens. Belongs to the SPTSS family. SPTSSB subfamily.