The retrotransposon known as long interspersed nuclear element-1 (L1) is 6 kb 
long, although most L1s in mammalian and other eukaryotic cells are truncated. 
L1 contains two open reading frames, ORF1 and ORF2, that code for an RNA-binding 
protein and a protein with endonuclease and reverse transcriptase activities, 
respectively. In this work, we examined the effects of full length L1-ORF2 and 
ORF2 fragments on green fluorescent protein gene (GFP) expression when inserted 
into the pEGFP-C1 vector downstream of GFP. All of the ORF2 fragments in sense 
orientation inhibited GFP expression more than when in antisense orientation, 
which suggests that small ORF2 fragments contribute to the distinct inhibitory 
effects of this ORF on gene expression. These results provide the first evidence 
that different 280-bp fragments have distinct effects on the termination of gene 
transcription, and that when inserted in the antisense direction, fragment 280-9 
(the 3' end fragment of ORF2) induces premature termination of transcription 
that is consistent with the effect of ORF2.