Transcription factor that specifically recognizes the sequence 5'-YAAC[GT]G-3' (PubMed:7813437, PubMed:23523368). Acts as a master regulator of male meiosis by promoting expression of piRNAs: activates expression of both piRNA precursor RNAs and expression of protein-coding genes involved in piRNA metabolism, such as PIWIL1 (PubMed:21750041, PubMed:23523368). The piRNA metabolic process mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins and governs the methylation and subsequent repression of transposons, which is essential for the germline integrity (PubMed:23523368). Transcriptional activator of SOX30 (PubMed:29848638). Component of the DREAM complex (also named LINC complex) at least composed of E2F4, E2F5, LIN9, LIN37, LIN52, LIN54, MYBL1, MYBL2, RBL1, RBL2, RBBP4, TFDP1 and TFDP2. The complex exists in quiescent cells where it represses cell cycle-dependent genes. It dissociates in S phase when LIN9, LIN37, LIN52 and LIN54 form a subcomplex that binds to MYBL2 (By similarity). Predominantly in the testis. Very low levels in the ovaries, spleen and brain. During embryogenesis it is predominantly expressed in several regions of the developing central nervous system and the urogenital ridge. Expression in the CNS is confined to the neural tube, the hindbrain, the neural retina and the olfactory epithelium, and coincides with the presence of proliferating immature neuronal precursor cells. In the adult mouse, A-Myb is expressed at high levels in type A spermatogonia (stem cells), and preleptotene and pachytene spermatocytes, with concomitant down-regulation of expression upon terminal differentiation of these cells into mature spermatozoa, and in B lymphocytes located in germinal centers of the spleen (PubMed:7813437, PubMed:8084617). Present in mid-late pachytene and diplotene spermatocytes, but not in late zygotene/early pachytene cells (at protein level) (PubMed:21750041).