DIFFERENTIAL EXPRESSION OF SEVERAL E2-TYPE UBIQUITIN CARRIER PROTEIN GENES AT DIFFERENT DEVELOPMENTAL STAGES IN ARABIDOPSIS-THALIANA AND NICOTIANA-SYLVESTRIS

We characterized three genes encoding different E2-type ubiquitin carr ier proteins involved in the ubiquitin-mediated proteolytic pathway: U bcAt3 shows homologies to the yeast CDC34 gene and UbcAt4a and UbcAt4b are two different genes homologous to the Ubc1/4/5 subfamily in yeast . Their accumulation was analysed and compared with that of the differ ent families encoding polyubiquitins, as well as the monoubiquitin fus ion protein, which is considered as a marker for cell division, during various developmental stages including G0/S transition and senescence of higher plant cells. Our results imply that these Ubc genes are und er the control of complex mechanisms, and are differentially regulated , but not necessarily co-regulated with ubiquitin genes. Even the clos ely related UbcAt4a and UbcAt4b genes of the same multigene subfamily are controlled by distinct regulatory mechanisms.