Poster: Protein Targeting & Vesicular Trafficking

Abs # 1175: Nuclear localization and in vivo dynamics of a novel plant-specific serine/arginine-rich protein

Presenter:	Ali, Gul S, gul.ali@colostate.edu
Authors	Ali, Gul S (A)   Golovkin, Maxim  (A)   Reddy, A.S. N (A)
Affiliations:	(A): Dept.of Biology, Colorado State University, Fort Collins, Colorado
Web Site:	http://lamar.colostate.edu/~reddy/index.html

We have previously demonstrated that SR45, a novel plant-specific serine/arginine-rich (SR) protein, interacts with U1-70K (one of the three U1 snRNP-specific proteins) and SR33 (an SC35 -like protein). Like other SR proteins, SR45 has both RNA recognition motif (RRM) and SR domain but is unique in having two SR domains, one at the amino-terminus and the other at the carboxy-terminus, separated by an RRM. The subcellular localization and dynamics of this protein are not known. To address these issues, we expressed SR45 as a fusion to green fluorescent protein (GFP) in cultured cells and transgenic plants. The GFP-SR45 fusion protein localized to nuclei in transiently transformed onion and tobacco BY-2 cells as well as in stably transformed Arabidopsis plants. In interphase nuclei, GFP-SR45 was distributed in a diffused pattern with areas of intense brightness of variable size and number that we refer to as speckles. These speckles exhibited localized intranuclear movements and changes in morphology. Upon inhibition of transcription by heat shock, actinomycin-D or a-amanitin, the SR45 relocalized to fewer bigger foci, indicating that the localization of SR45 is controlled by transcription. Treatment with staurosporine, an inhibitor of protein kinase, also resulted in few larger speckles. Interestingly the change in the number and morphology of speckles caused by actinomycin-D and heat were inhibited by okadaic acid, an inhibitor of phosphatase. These results indicate that transcription activity of the cell and protein (de)phosphorylation regulate the intranuclear distribution of the Arabidopsis SR45