| Autor: |
Wilson, N F, O'Connell, J S, Lu, M, Snell, W J |
| Zdroj: |
Journal of Biological Chemistry; November 1999, Vol. 274 Issue: 48 p34383-8, 6p |
| Abstrakt: |
During fertilization in Chlamydomonas, flagellar adhesion between mt(+) and mt(-) gametes induces a cAMP-dependent signal transduction pathway that prepares the gametes for cell fusion and zygote formation. Previously, our laboratory identified a homeodomain protein (GSP1) whose expression was restricted to the cell bodies of mt(+) gametes and whose transcript level was up-regulated during flagellar adhesion. In this report, we describe a new form of GSP1 that appears early during gamete interactions. Immunoblot analysis showed that in addition to the 120-kDa form of GSP1 normally present in mt(+) gametes, a 122-kDa form was detected when the cells were mixed with mt(-) gametes. The more slowly migrating form of GSP1 was detectable within minutes after gametes were mixed together, and its appearance did not require new protein synthesis. Thus, the 122-kDa form represents a post-translational modification of the pre-existing 120-kDa form of GSP1. Moreover, conversion to the 122-kDa form did not require cell fusion. Although the 120-kDa form was expressed 10 h after vegetative cells were transferred to gametic induction medium, the 122-kDa form was detected only after mt(+) gametes were induced to undergo the sexual signaling that accompanies fertilization. Incubation of mt(+) gametes with dibutyryl cAMP led to the appearance of the 122-kDa form of GSP1, and the cyclic nucleotide-dependent protein kinase inhibitor H-8 inhibited the adhesion-induced conversion. Incubation of GSP1 immunoprecipitated from signaling mt(+) gametes with alkaline phosphatase showed that the conversion was due to phosphorylation. The results indicate that flagellar adhesion induces a rapid, cAMP-dependent phosphorylation of the homeodomain protein GSP1 early during fertilization in Chlamydomonas. |
| Databáze: |
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