jumping gene

transposable element

transposition

transposon

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Transposable elementtransposon

Inverted repeats, palindrome transposase

Direct repeats

Tn5: Kanr

Tn10: Tetr

Replicative transposition: Tn3

nonreplicative transposition: Tn10

MaizeBarbara McClintock

Figure 23.9

Retrotransposonsretroviruses

RNase Hdegrades the RNA partof an RNA-DNA hybrid

LTR-containing retrotransposons

• Copia of Drosophila: 1% of the total fruit fly genome

• Ty of yeast

• Human endogenous retroviruses: 1-2% of the genome

Non-LTR retrotransposons

long interspersed elements (LINES) L1: 17% of the human genome

EN: endonuclease RT: reverse transcriptase

Nonautonomous retrotransposonsencode no protein

• Alu elements contain the sequence AGCT that is recognized by the restriction enzyme AluI. They are present in up to a million copies in the human genome.

• They can not transpose by themselves. Instead they take advantage of the retrotransposition machinery of other elements, such as LINEs.

retrohoming

retrotransposition of group II intron