PHYTOCHROME REGULATES GTP-BINDING PROTEIN-ACTIVITY IN THE ENVELOPE OFPEA NUCLEI

Three GTP-binding proteins with apparent molecular masses of 27, 28 an d 30 kDa have been detected in isolated nuclei of etiolated pea plumul es. After LDS-PAGE and transfer to nitrocellulose these proteins bind [P-32]GTP in the presence of excess ATP, suggesting that they are mono meric G proteins. When nuclei are disrupted, three proteins co-purify with the nuclear envelope fraction and are highly enriched in this fra ction. The level of [P-32]GTP-binding for all three protein bands is s ignificantly increased when harvested pea plumules are irradiated by r ed light, and this effect is reversed by far-red light. The results in dicate that GTP-binding activity associated with the nuclear envelope of plant cells is photoreversibly regulated by the pigment phytochrome .