Figure 1.

There is a single phosphorylation site, Ser-10, in the N terminus of Tetrahymena micronuclear H3. (A) HPLC-purified H3 from either macro- or micronuclei of logarithmically growing Tetrahymena cells labeled in vivo by [³²P]orthophosphate was resolved on a 12% SDS/PAGE gel and examined by Coomassie blue staining (Left) or autoradiography (Right). (B) In vivo phosphorylated micronuclear H3 was subjected to automated sequencing from the N terminus, and ³²P radioactivity eluted from each sequencing cycle was collected and counted. Note that an identical conclusion was reported previously by us as an unpublished observation (26).