6th March - All Splicing involves selection among alternative possibilities

Question 1

What percentage of protein coding genes contain introns?

Answer 1

96%

Question 2

What percentage of intron containing protein coding genes produce multiple splicing isoforms?

Answer 2

95%

Question 3

Approximately how many isoforms of mRNA are expressed per gene?

Answer 3

About 7 (up to 11/12)

Question 4

What is LSD1?

Answer 4

A histone demethylase which normally demethylates H3K4 me1/2 and H3K9 me1/2

Question 5

What is LSD1+8a?

Answer 5

A neuron specific isoform of LSD1 which demethylates H3K9me2 along with supervillin

Question 6

What are the different isoforms of BCL-X?

Answer 6

BCL-XL = Anti-apoptotic
BCL-XS = Pro-apoptotic

Question 7

What is neurexin 3?

Answer 7

A protein which prevents shortcircuiting in a growing axon, which has many isoforms

Question 8

How is alternative splicing related to organismal complexity?

Answer 8

Organismal complexity seems to have evolved with alternative splicing

Question 9

What are micro exons?

Answer 9

Exons <30/20nt thus too small to form its own protein domain

They are located on the outside of an existing domain therefore affect protein interactions

Question 10

What are the factors affecting splice site usage?

Answer 10

Splice site sequences
Intron length
Exon sequences
Secondary structure
Transcription

Question 11

How was SMI used to determine the order of spliceosome assembly?

Answer 11

Used co-localisation single molecule spectroscopy (CoSMoS)
Tethered pre-mRNA in S. cerevisae whole cell extract
Used three way CoSMoS
Showed U1 binding was highly dynamic
–> Confirmed U1 –> U2 –> U5.U4/U6 –> NTC pathway

Showed U1 and U2 binding occurs on a branched pathway