An analog of Xenopus N1N2 protein in Pleurodeles waltl.

The oocyte nucleus of Pleurodeles waltl contains a major 185-kDa protein analog of Xenopus N1N2. Rabbit antibodies were raised against the 185-kDa protein. Affinity-purified antibody directed against the acid part (pI 4.7) of the protein was prepared using antigens separated by two-dimensional electrophoresis. Specificity of the antibody was controlled on two-dimensional gels of nuclear proteins. It was shown that the 185-kDa protein was separated into 2 forms: an acid form of pI 4.7-5.3, and a base form of pI 7. Peptide maps of the 2 spots revealed that they were closely related. The antibody was tested on: a) spread nuclear content, b) on sections of embryonic stages from stage 2 to stage 34, and c) the sections of adult tissues. The 185-kDa protein appeared to be associated with the RNP matrix of a particular type of lampbrush chromosome loop, the granular loop. This protein was present in the nuclei of all embryonic cells. In adult tissues, it was present only in the nuclei of cells which presented high mitotic activity. These results confirm that, like N1N2, the 185-kDa protein interacts with the constitution of chromatin; furthermore, they provide evidence for the role of this protein in transcriptional activity.