The Nature of Transposons Chapter 11 pp

Outline Nature of Transposons Transposons –Prokaryotic –Eukaryotic: Dr. McClintock’s research Retrotransposons vs Retroviruses

Transposons Are mobile DNA sometimes referred to as “jumping genes”.

Common features associated with transposons 1. Direct repeats 2. Terminal Inverted repeats Common Features Are:

Transposable Elements in Bacteria

1. Simple Bacterial Transposon INSERTION SEQUENCE

2. COMPOSITE TRANSPOSON IS + any DNA segment

Dr. Barbara McClintock Nobel Prize, 1983 Physiology or Medicine

“I don’t understand a word that she said, but if she says it is so, it must be so!” Alfred Sturtevant

“Ds Transposed out”

The Ds element often results in chromosomal breakage

Drosophilia melanogaster & DNA transposition “The P Element”

The P element Codes for Transposase Repressor of transposition

Offspring sterile Offspring normal Why the difference? Female P- and male P+ Female P+ and male P- Hybrid dysgenesis Non-hybrid dysgenesis

Remember the P element Codes for A Transposase AND A Repressor of transposition

Mite Science Sep 6;253(5024): Possible horizontal transfer of Drosophila genes by the mite Proctolaelaps regalis. Houck MA, Clark JB, Peterson KR, Kidwell MG. Houck MAClark JBPeterson KRKidwell MG D. melanogaster D. willistoni The P element took a ride on a That moved it onto ~50 yrs ago

Retrotransposons mRNA DNA

Examples of retrotransposons elements Ty Copia Alu Yeast Drosophila Humans

General Mechanism Of Retrotransposons Note: retrotransposons are not found in prokaryotes

Types of Retrotransposons Ty Copia Yeast Drosophila Humans Viral Non-Viral Alu

Non-viral Retrotransposons Humans Non-Viral LINES SINES AluExample:Line 1 and Line 2

ALU 300 bp Endonuclease cutting site: site5' AG/CT 3‘ Retrotransposon 1 million in genome Linked to variety of disorders

Alu has inserted in NF-1 gene Neurofibromatosis: autosomal dominant Growth of nodules mainly affecting nerves in the skin

Viral retrotransposons look a little like retroviruses—but are NOT the same !

Now we must compare a Viral RNA with a Viral Retrotransposon

VIRAL RNA

Infectious process

Now a viral retrotransposon

Here’s the Copia element of Drosophila Compare to the retrovirus Similar gag and pol sequences

Here’s the Ty element, again notice similarities to retroviruses Delta sequences function like LTR’s in viruses

Summary Table Viral and non-viral Ty and Copia viral retrotransposons Alu non viral retrotransposons

A topic of scientific discussion is what is a “prion”?

Blunt cut from donor

HUMAN IMMUNODEFICIENCY VIRUS Human Helper T Lymphocyte