what aa are good as linker sequences in mammals - (Jul/25/2007 )

hey everyone,
I'm designing my own MCS to insert into a plasmid. Does anyone have any tips on what AA's i should avoid and which would be good for linking my restriction sites ( this will be expressed in mammlian cells)

Thanks,
joe

well take example of the pIRES Neo vector for example. It's for protein production in mammals.