Figure 3: Mechanisms of insertional mutagenesis. (1) 3’ proviral LTRs can drive over-expression of nearby genes. (2) Enhancers in the LTRs can activate nearby promoters leading to increased transcription. (3) Proviral insertion within a host gene and transcription from the 5’ LTR can lead to the creation of novel gene transcripts. (4) Premature polyadenylation of host cell gene transcripts can be caused by proviral insertion within a gene. Black boxes represent the host gene promoter and grey squares represent the exons. Grey boxes containing white rectangles represent proviral LTRs and striped rectangles are used to show proviral transgenes.