HEAB is a 425 amino acid nuclear protein that belongs to the Clp1 family. Utilizing magnesium, manganese or nickel as cofactors, HEAB participates in the phosphorylation of the 5'-hydroxyl groups of double- and single- stranded RNA and DNA. HEAB is a member of the tRNA splicing endonuclease complex, in conjunction with TSEN2, TSEN15, TSEN34 and TSEN54, and is also a member of the pre-mRNA cleavage complex II. The gene encoding HEAB maps to human chromosome 11q12.1 and mouse chromosome 2 D