[BioC] AffyID mapping question

[Jiayi Hou [guest]]

I am working on a project trying to mapping Affymetrix probeset ID to Entrez ID, Gene Symbol and its chromosomal location. I used R package biomaRt and another one named mouse4302.db for Affymetrix Mouse430 2.0 array specifically. I noticed from the result, for genes have multiple probesets attached, only a small proportion of these probesets have a precise transcription start locations. While most of these probesets share the same start location with the given gene. Is there anyway I can get a better match in terms of the precise transcription start location for each probeset? 

 -- output of sessionInfo(): 

R version 2.12.2 (2011-02-25)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252 
[2] LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] mouse4302.db_2.4.5   org.Mm.eg.db_2.4.6   RSQLite_0.10.0      
[4] DBI_0.2-5            AnnotationDbi_1.12.1 mouse4302cdf_2.7.0  
[7] affy_1.28.1          Biobase_2.10.0       biomaRt_2.6.0       

loaded via a namespace (and not attached):
[1] affyio_1.18.0         preprocessCore_1.12.0 RCurl_1.5-0.1        
[4] tools_2.12.2          XML_3.2-0.2  

--
Sent via the guest posting facility at bioconductor.org.