[BioC] about filtering genes from exprSet by names

[yanju]

Dear Bioconductors,

Now my problem is as follows:
First of all, I read the microarray .gpr files to RGlist, then  
normalized it to MAlist. After that I convert the MAlist to exprSet for 
further analysis. Now, I want to filter genes in exprSet according to 
the names or probeID, but I found there is no geneNames Slot for my 
exprSet. How to find or keep the geneNames or ID for each genes? And how 
to filter by gene names? my partial code is like follows:

rg<-read.maimages(...)
ma.p<-normalizeWithinArrays(rg)
ma.paq<-normalizeBetweenArrays(ma.p)
exp<-as(ma.paq, "exprSet")
 > geneNames(exp)
NULL
????
Or other approaches or suggestions?

Thanks

Regards,
Yanju