Enables SH3 domain binding activity. Involved in several processes, including positive regulation of myeloid leukocyte differentiation; positive regulation of tyrosine phosphorylation of STAT protein; and regulation of transcription by RNA polymerase II. Located in cytoplasm and nucleus. Is expressed in thymus primordium. Orthologous to human HCLS1 (hematopoietic cell-specific Lyn substrate 1). [provided by Alliance of Genome Resources, Apr 2022]