IMPORT OF TOBACCO MOSAIC-VIRUS COAT PROTEIN INTO INTACT CHLOROPLASTS INVITRO

Tobacco mosaic virus coat protein (TMV CP) bas been found in chloroplasts. However, there is evidence that chloroplasts from infected plants do not synthesize CP under conditions in which active protein synthesis can be shown in organello (A. Reinero and R. N. Beachy, Plant Physiol. 89:111-116, 1989). Here, in vitro-labeled TMV CP is shown to be imported into isolated, intact chloroplasts even though it does not have a recognizable transit sequence. Within the chloroplast, some of the labeled CP is found as higher molecular weight forms. The import is not dependent on protease-sensitive outer membrane receptors, and it does not require ATP. The CP is imported very rapidly and is found almost exclusively in the thylakoid membrane fraction of the chloroplast.