Recived 6/10/97; Accepted 7/1/97

2. INTRODUCTION

Differential display was developed as a method to identify differences in gene expression among eukaryotic cells. (1) Different primer combinations are used in a reverse transcriptase-polymerase chain reaction (RT-PCR) to generate cDNAs from mRNAs expressed in a given cell. By comparing the cDNAs derived from multiple cell types, or from a single cell type under different conditions, it is possible to detect differences in transcription products derived from the different conditions. These differentially expressed products are identified on an acrylamide gel, excised, eluted, re-amplified,and eventually sequenced (2, 3, 4 ). This process can be technically challenging at a number of steps, and loss of a differentially expressed band because of failed attempts at reamplification can be particularly frustrating.

In our laboratory, attempts to reamplify DNA sequences cut from a denaturing 6% acrylamide gel consistently failed when greater than 5 microliters of eluted product was used as template in a subsequent PCR reaction.