Genomic Repetitive Elements (Human Focus)

TYPES OF ELEMENTS Tandem repeats: a) satellite DNA 1) centromeric and heterochromatic 2) minisatellite 3) 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 retrotransposons THE1, copia, Ty Class II retro- transposons loss of LTR loss of env loss of pol (RT)

Viral Envelope Protein Matrix Integrase Protein Reverse Transcriptase Nucleocapsid Viral RNA genome Capsid pol gag envLTR Retrovirus 10 KB in size

Nuclear Translocation Retrovirus Replication Cycle Virus Entry Uncoating & Reverse Transcription Integration into host 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 OvumSperm 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 transcriptase Endonuclease 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 EVOLUTIONARY CONSEQUENCES OF THESE MOBILE ELEMENTS?