CKI, in vitro phophorylation

[Anna Bigas]

I am trying to perform "in vitro phosphorylation" assays with Casein
kinase I and a GST-fusion protein. I am having a great deal of problems
getting my negative control (no enzyme) phophorylated. This also happens
when I use casein as  a substrate. If I increase the amount of cold ATP,
all signs of phophorylation disapear.

Does anybody have a protocol for phosphorylation of casein by CKI? or
any other helpful advise for "in vitro phosphorylation".  This is a
whole new world to me.

Thank you very much.