Filter hybridization efficiency

[FRANK,BART]

We have been typing PCR products from different individuals using
labelled oligonucleotide probes.  When we separate the PCR products
using a PAGE, and electrotransfer the DNA to a nylon filter, hybridize,
& wash, a typical autoradiograph exposure time is 30 minutes.  If we
take the PCR products and transfer them to the same type of membrane 
using a vacuum (dot blot/slot blot, no electrophoresis), the typical
exposure time is 3-4 hours.  Can you explain this difference?  The
same amount of PCR products are used in both cases.

Bart Frank, Ph.D.
Arthritis and Immunology Program
Oklahoma Medical Research Foundation
Internet: BFRANK at AARDVARK.UCS.UOKNOR.EDU