115-KDA PROTEIN FROM XENOPUS-LAEVIS EMBRYOS RECOGNIZED BY ANTIBODIES DIRECTED AGAINST THE XENOPUS HOMEOPROTEIN XIHBOX-1

Using antibodies against homeoprotein XlHbox 1 from Xenopus laevis, we have detected a new embryonic protein with a much larger molecular we ight, 115 kDa. Antibodies fractionated according to their affinity for 3 different domains of the XlHbox 1 protein were used to show that th is new protein is related to the C-terminal region of XlHbox 1 protein , downstream from the homeodomain. By immunohistochemistry, the protei n was shown to be localized in nuclei of embryonic cells. On SDS-polya crylamide gels, the 115 kDa protein appears as a set of closely spaced bands whose pattern varies with the stage of development and with the parental origin of the embryos. The protein could be extracted from e mbryos in a multiprotein complex of approximately 600 kDa. In contrast , the 18 and 27 kDa proteins predicted from the sequence of cloned cDN A to be transcribed and translated from the XlHbox 1 gene could not be detected, suggesting that they are rare or unstable in embryos. These data suggest that the new protein is involved in the development of X enopus embryos, with a function possibly related to that of the homeop rotein XlHbox 1.