Characterization of 26S proteasome alpha- and beta-type and ATPase subunits from spinach and their expression during early stages of seedling development.

Three kinds of cDNAs encoding 26S proteasome subunits have been cloned from spinach (Spinacia oleracea L.). These genes, designated as SOPSC8, SOPSC1 and SOPRS7, encode an alpha-type and a beta-type subunit of the 20S catalytic core, and an ATPase subunit of the 19/22S regulatory complex, respectively. The deduced protein sequences showed high sequence similarities to other proteasome alpha- and beta-type and ATPase subunit proteins. Southern blot analysis indicates that there are additional members of these dispersed proteasome families in the spinach genome. These three subunit genes are expressed simultaneously during germination and reach a maximum one day after sowing followed by a decline. The expression of these genes also increases during cotyledon senescence.