Constitutively active serine/threonine-protein kinase that exhibits growth-factor-independent kinase activity and that may participate in p53/TP53-dependent cell growth arrest signaling and play an inhibitory role during embryogenesis. {ECO:0000269|PubMed:15042092, ECO:0000269|PubMed:15632195}. This is the function of Ensembl gene identifier ENSG00000072133 (RPS6KA6, ribosomal protein S6 kinase A6).