The Nature of TransposonsChapter 11 pp 297-309

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

CommonFeatures

Are:

Transposable Elements in Bacteria

1. Simple Bacterial Transposon

INSERTION SEQUENCE

2. COMPOSITE TRANSPOSONIS + any DNA segment

Dr. Barbara McClintock1902-1992

Nobel Prize, 1983Physiology 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 norm

al

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. 1991 Sep 6;253(5024):1125-8Possible horizontal transfer of Drosophila genes by the

mite Proctolaelaps regalis.

Houck MA, Clark JB, Peterson KR, Kidwell MG.

D. melanogaster

D. willistoni

The P element took a ride on a

That moved it onto

~50 yrs ago

Retrotransposons

mRNADNA

Examples of retrotransposons elements

• Ty

• Copia

• Alu

Yeast

Drosophila

Humans

General MechanismOf 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

Alu Example: 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 dominantGrowth 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-viralTy and Copia viral retrotransposons

Alu non viral retrotransposons

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

Blunt cut from donor

HUMANIMMUNODEFICIENCYVIRUS

Human Helper T Lymphocyte