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Group II Self-Splicing Introns. -pre-rRNA of fungal and plant mitochondria -majority of chloroplast introns -several classes -require Mg 2+ -no cofactor. Domain Structure of a Group II Intron. A. 5’ exon. 3’ exon. Chemistry of Group II Self-Splicing. 1st step. 2nd step. lariat.

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Group II Self-Splicing Introns

-pre-rRNA of fungal and plant mitochondria

-majority of chloroplast introns

-several classes

-require Mg2+

-no cofactor


Group II Self-Splicing

Lariat Formation

electron micrograph of Group II lariat

Genes VII


Group II X-ray

Science 2008 320 77 - 82


“Homing” Endonucleases

-some Group II introns contain ORF for DNA endonuclease

activity and reverse transcriptase (RT)activity


“When the junk isn’t junk”

Nature (1996) 379, 402-3

-snoRNAs (small nucleolar) involved in RNA transcription

-nucleoli are sites of rRNA transcription, processing , ribosomal subunit


-U22 snoRNA host gene (UHG)

-exon sequences not conserved between species, introns conserved




RNase P

E. coli RNase P - the activity responsible for the maturation of

the 5’ end of pre-tRNAs contains a protein component (C5) and an

RNA component (M1)


RNase P X-ray

Proc Natl Acad Sci(2005) 102, 13392


E. coli Ribosome

-70S particle, MW ~2.5 x 106

-dissociable into small (30S) and large (50S) subunits

-30S contains 16S RNA, 21 polypeptides

-50S contains 5S, 23S RNA + 31 polypeptides

“Although the ribosome has been crystallized…it is such

a complex entity that it will be many years before its

structure is known in molecular detail”

- Voet and Voet, Biochemistry 1995


Ribosome X-ray Structure

Science (2000) 289:920-30