Fig. 7. Phosphorylated Sec63p is only slowly turned over. (A) Wild-type or cka2ts cells were shifted to the restrictive temperature, pulsed at the indicated times with [³⁵S]-methionine and subjected to CPY immunoprecipitation (upper panel). Extracts of the same cells were also probed for the presence of the phosphorylated Sec63p by the Sec62_C125-Dha overlay assay (lower panel) (B) Summary. Newly made Sec63p is rapidly phosphorylated by protein kinase CK2. The phosphorylated Sec63p binds strongly to Sec62p and becomes protected against dephosphorylation. Certain conditions might induce a phosphatase activity that dephosphorylates Sec63p and thereby shifts the ratio from the bound to the free form.