The secondary structures in mRNA often cause early termination during the synthesis of cDNA. In an attempt to determine the 5'-untranslated region (UTR) of the gene LIP1 using the RNA ligase-mediated rapid amplification of cDNA ends (RLM-RACE), we found that reverse transcriptases skipped over the LIP1 RNA secondary structures and continued the DNA synthesis through RNA adapter sequences without early termination. A fragment of only three nucleotides upstream of the LIP1 translation initiation codon was obtained from the initial RACE-PCR, which was much shorter than the 57-nucleotide fragment obtained from the cDNA library screening. Analysis of the 5' end sequence indicates the presence of high G+C content and stem-loop secondary structures. Therefore, optimizations of the reaction with high temperature (70 degrees C) and a thermostable reverse transcriptase were performed to synthesize the first-strand cDNA, which was determined to have 73 nucleotides in the 5'-UTR. These results suggest that, under cDNA synthesis conditions at 42 degrees C and 60 degrees C, the reverse transcriptases skipped over the stem-loop structures of LIP1 mRNA and continued the cDNA synthesis until they reached the RNA adapter sequences. Thisfinding draws attention to adopting optimized conditions for cDNA synthesis on G+C-rich RNA templates.