A NOVEL 77-RESIDUE PEPTIDE FROM PORCINE BRAIN CONTAINS A LEUCINE-ZIPPER MOTIF AND IS RECOGNIZED BY AN ANTISERUM TO DELTA-SLEEP-INDUCING PEPTIDE

In 1977 a nonapeptide, called delta-sleep-inducing peptide (DSIP) was characterized in rabbit cerebral venous blood plasma during thalamic s timulation to induce sleep. Evidence for the existence of DSIP in the central nervous system and in numerous peripheral organs of various ma mmalian species has been obtained using immunochemical techniques. Lat er findings have revealed the existence of large forms of DSIP-like im munoreactivity. We decided to investigate the molecular identity of su ch large forms of DSIP-like immunoreactivity by direct isolation. We h ave purified and characterized using amino acid analysis, sequencing, mass spectrometry and radioimmunoassay a 77-residue peptide, denoted D IP (DSIP-immunoreactive peptide), from an acid extract of porcine brai n. DIP is recognized by an antiserum raised against synthetic rabbit D SIP. The amino acid sequence of DIP, however, is not related to that o f DSIP, but it contains a putative leucine-zipper motif, a proline/glu tamic-acid-rich domain, three potential phosphorylation sites and exhi bits an acetylated N-terminus. The N-terminal but not the C-terminal p art of the newly isolated peptide shares clear homology with the seque nce of a protein induced by transforming growth factor beta1 and other growth factors in mouse osteoblastic cells. DIP is also structurally similar to a baculoviral protein p10. The function of DIP remains uncl ear but its involvement in transcriptional regulation is probable.