SET Domain Containing Protein 1B (SETD1B)

SET1B is a component of a histone methyltransferase complex that produces trimethylated histone H3 at Lys4. Like SET1A, SET1B contains conserved SET and post-SET domains in the C terminus and an RNA recognition domain in the N terminus, but it lacks the HCF1-binding motif of SETD1A.

In vitro assays demonstrated that the SET1B complex is a histone methyltransferase that produces trimethylated histone H3 at Lys4. Inducible expression of the C terminus of either SET1A or SET1B decreased steady state levels of both endogenous SET1A and SET1B protein, but did not alter the expression of the noncatalytic components of the SET1 complexes. Confocal microscopy revealed that the SET1A and SET1B proteins localize to a largely nonoverlapping set of euchromatic nuclear speckles.