Krüppel-related zinc finger proteins probably constitute the largest individual family of transcription factors in mammals. These proteins often carry a potent repressor domain called the Krüppel Associated Box (KRAB), which is known to effectively repress transcription through interaction with transcriptional intermediary factor 1beta (TIF1beta). Here we report the isolation and characterization of a novel human KRAB A zinc finger protein, HZF12. The gene encoding HZF12 is located on Chromosome (Chr) 19p13.11-p12, and a 4.4-kb transcript from this gene is expressed in a variety of adult and fetal tissues. Two additional, larger transcripts are expressed in testis only. Interestingly, the KRAB A domain of HZF12 is followed by a 21-amino acid domain, encoded by a separate exon. This domain, which we designate KRAB C, was also identified in more than 25 additional human, mouse, and rat KRAB zinc finger proteins. On the basis of results from a previous study, we conclude that this novel KRAB domain strengthens the interaction with TIF1beta, thereby improving the ability of these KRAB zinc finger proteins to recruit TIF1beta to specific sites.