The Integrase of the Long Terminal Repeat-Retrotransposon Tf1 Has a Chromodomain That Modulates Integrase Activities

Department of Cell and Developmental Biology, Tel Aviv University, Tell Afif, Tel Aviv, Israel
Journal of Biological Chemistry (Impact Factor: 4.57). 12/2005; 280(47):39086-94. DOI: 10.1074/jbc.M506363200
Source: PubMed


Chromodomains in a variety of proteins mediate the formation of heterochromatin by interacting directly with histone H3, DNA,
or RNA. A diverse family of long terminal repeat (LTR)-retrotransposons possesses chromodomains in their integrases (IN),
suggesting that the chromodomains may control integration. The LTR-retrotransposon Tf1 of Schizosaccharomyces pombe is highly active and possesses a chromodomain in the COOH terminus of its IN. To test this chromodomain for a role in integration,
recombinant INs with and without the chromodomain were assayed for activity in in vitro reactions. The full-length IN had integration activity with oligonucleotide substrates that modeled both the insertion reaction
and a reverse reaction known as disintegration. The INs of retroviruses possess an additional activity termed 3′ processing
that must remove 2-3 nucleotides from the 3′ ends of the viral cDNA before insertion can occur. These additional nucleotides
are added during reverse transcription because of the position of the minus strand primer downstream of the LTR. The position
of the primer for Tf1 suggests no nucleotides are added 3′ of the LTR. It was therefore surprising that Tf1 IN was capable
of 3′ cleavage. The most unexpected result reported here was that the IN lacking the chromodomain had significantly higher
activity and substantially reduced substrate specificity. These results reveal that both the activity and specificity of enzymes
can be modulated by their chromodomains.

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