Autofluorescence and GFP fusions

[P E Sudbery]

We are trying to localise the intracellular location of a 
S.cerevisiae protein using a GFP fusion. Trouble is our negative 
controls fluoresce like crazy. We have tried W303 and Berkeley strains 
and have grown cells on YEPD and minimal media. Washing cells with 
phosphate buffer helps but doesn't eliminate the problem. We don't 
think its our microscope because we have also used  GFp fusions in 
Candida albicans without any problems. Anybody got any ideas?