SCL, also known as Tal1 (T cell acute lymphocytic leukemia-1 protein), is a basic helix-loop-helix transcription factor. It regulates hematopoiesis, angiogenesis, and erythrocyte maturation. Activation of SCL by chromosomal translocation may be associated with T cell acute lymphoblastic leukemia. Human and mouse SCL share 93% amino acid sequence identity.