The ubiquity of the highly phosphorylated nuclear protein P1

The present work shows that antibodies raised in rabbits against rat liver P1 confirmed the presence of P1 in lung, kidney, brain heart, muscle, intestine and thymus in rats. The antiserum reacted with P1 from human and monkey but not from bovine, pig and mouse P1 in spite of there being a close relationship in amino acid composition, electrophoretic properties and peptide mapping. Proteolytic digestion of rat P1 showed that only some of the peptides produced reacted with the antiserum, suggesting that conformational determinants may be dominating compared to sequential determinants in P1, or that only minor parts of P1 which exhibit sequential variation between species are immunoreactive.