Genomic Repetitive Elements(Human Focus)

TYPES OF ELEMENTS

Tandem repeats:a) satellite DNA

1) centromeric and heterochromatic2) minisatellite3) microsatellite

b) telomers

Interspersed repetitive elements:a) transposons

1) Class I – copy and paste (RNA intermediate)a) retrotransposons (no envelope protein)b) Long Interspersed Nuclear Elements (LINES)c) Short Interspersed Nuclear Elements

(SINES; example: Alu)2) Class II – cut and paste (DNA element)

b) Endogenous Retroviruses (ERVs) (contain Envelope Proteins)

Relationship of retroelements

Retroelements

Retroviruses

Class I retrotransposonsTHE1, copia, Ty

Class II retro-transposons

loss of LTR

loss of env

loss of pol (RT)

Viral Envelope Protein

Matrix

Integrase Protein

Reverse Transcriptase

NucleocapsidViral RNA genome

Capsid

polgag envLTR LTR

Retrovirus

10 KB in size

Nuclear Translocation

Retrovirus Replication Cycle

Virus Entry

Uncoating & Reverse Transcription

Integration intohost genome

Transcription

Translation

Release &Maturation

Assembly

FOR RETROVIRUSES REVERSE TRANSCRIPTION . . .

A) OCCURS IN THE CYTOSOL

B) USES A t-RNA PRIMER TO INITIATE REVERSE TRANSCRIPTION

Retroviruses

Somatic CellsGermline Cells

e.g., liver cells

virus NOT passed on to progeny

Ovum Sperm

virus passed on to progeny

Endogenous Retrovirus (ERV) Exogenous Retrovirus

Infection leads to

integration of retrovirus

genome into the host genome

Germline Cells

Repeated infections in the germline are referred to as “expansions”

LINES AND SINES

LINE Proteins:Orf 1 – RNA binding protein

Orf2 – Reverse transcriptaseEndonuclease activity

FOR LINES AND SINES REVERSE TRANSCRIPTION . . .

A) OCCURS IN THE NUCLEUS

B) USES THE NICKED DNA TO INITIATE REVERSE TRANSCRIPTION

WHAT ARE THE GENOMIC AND EVOLUTIONARYCONSEQUENCES OF THESE MOBILE ELEMENTS?