Predicted to enable several functions, including 7SK snRNA binding activity; P-TEFb complex binding activity; and cyclin-dependent protein serine/threonine kinase inhibitor activity. Acts upstream of or within heart development and negative regulation of transcription, DNA-templated. Located in nucleus. Is expressed in several structures, including branchial arch; embryo mesenchyme; heart and pericardium; hindgut dorsal mesentery; and sensory organ. Orthologous to human HEXIM1 (HEXIM P-TEFb complex subunit 1). [provided by Alliance of Genome Resources, Apr 2022]