Figure 1

Effects of repeated sequences on gene expression. (a) An open reading frame (cyan rectangle) with a repetitive region (dark-blue stripes) is transcribed from an upstream promoter (dotted line and arrowhead). 1, Replication slippage leads to a frameshift with a new stop codon (indicated by the cross over the open reading frame). 2, Replication slippage or unequal recombination can increase the number of repeats. (b) A mobile element (magenta gradient shading) is cut from between two genes (cyan and purple rectangles) by transposase (scissors). An error in repair after transposition introduces a chromosome break, which is repaired to give new telomeres (circles). (c) Recombination between homologous mobile elements on two different chromosomes leads to a translocation. (d) Effects of a mobile element (here shown with its own promoter and transcription) on gene expression. 1, An insertion within an open reading frame results in a truncated protein. 2, An insertion at the beginning of an open reading frame can result in large amounts of a fusion protein. 3, The presence of the retroposon or transposon promoter can activate the transcription of a downstream gene, for example by opening the chromatin. 4, Insertion in an opposite orientation results in antisense RNA. 5, Insertion in a 3'-untranslated region can affect mRNA processing, stability or translation. The example shown has normal monocistronic transcription; for kinetoplastids, transcription is polycistronic (not shown).