can you introduce mutation directly into the cells? - other than just transfecting it with a vector... (Feb/13/2006 )

hello everyone... i have strange question...im new to genetics and was thinking about one thing....can I introduce mutation directly into the protein in some cell type... ....i mean not to mutate some protein then trasfect it into vector then transfect into cells and see the overexpression result....just introduce some mutation directly into the endogenous protein in the cell to see the effect.....any methods to do that...am I dreaming?

There are a lot of methods to induce mutations, but only random mutations. Think about UV-light and some chemicals.
But to introduce a site-directed mutation, you really have to get a double-cross-over event at DNA-level.