Unit III" Translation

Molecular Genetics BIO431/531

What 2 gene expression types control the level of expression for the trp operon?

1. Global Control

   When trp (level) are high … gene expression is repressed by trpR (a repressor that binds to an operator)

2. Attenuation

   (fine-tuned control)

What parts of the dies the trp mRNA leader seq contain?

1. An attenuator region (ends prematurely)

   Can be controlled through STEM loop location

2. 2 trp codons

Draw STEM Loop when trp is high? Does transcription terminate or continue

What two locations can mRNA leader stem loops alternate from to manage attenuation for trp?

• High Level of trp= stem loop between 2 & 3 domain

  =TERMINATION of transcription

• Low level of trp = STEM loop btwn 2 & 3

  • Ribosome gets stalled at trp codon

    = TRANSCRIPTION CONTINUES

Describe function of guanine switch

Guanine in stem loop keeps ribosome off from transcription, remove the guanine in the stem loos transcription turns on

Describe the four mechanisms for alternative splicing

1. optional exon

   an exon is spliced into the mRNA strand

2. optional intron

   skipped on intron & kept in coding seq

3. mutually exclusive exons

   exons get spliced together & placed in the coding strand

4. internal splice site

   splicing within the intron is altered

Define Isoform

Different proteins translated using the same mRNA strand although have different splicing patterns

Evidence for isoform recognition

Isoforms of the same splicing patterns in dendrites repel from each other in self avoidance

isoforms of different splicing patterns in dendrites branches attract to each other

Mechanism of RNA Splicing

What are the steps to RNA transcription cleavage to produce a membrane bound lymphocyte is this long or short transcription?

Long transcription

1. Cleave mRNA sequence after 3’ splice acceptor site

2. Remove introns w/ RNA Processing

3. Commit to translation

4. Make membrane bound B lymphocyte w/ production of terminal hydrophobic peptide = MEMBRANE BOUND B LYMPHOCYTE

SHORT Transcription

1. Cleave before the 5’ for short transcript

2. DO NOT SPLICE the introns because the splice junction is mission

3. Translation w/o splicing intron

4. Congrats you secreted Protein Lymphocyte w/ high CstF

RNA Editing

What are the steps to produce a secreted antibody? Is this long of short transcription?

Membrane bound antibody is produced through a hydrophobic terminal protein & long transcription

What are the steps to RNA transcription cleavage to produce a secreted antibody is this long or short transcription?

A secreted antibody is produced by a short RNA transcript

Steps in antibody secretion for CstF

1. Cut the RNA transcript after the 5’ end

2. Do not remove introns

3. Translate

4. You have secreted antibody with protein lymphocyte

Describe how RNA edits itsself

Guide RNAs

Guide RNA 1 have nucleotides in guide RNA specifying missing U nucleotides

Guide RNA 2 (with its ‘disposible’ poly U tail) pairs with the mRNA transcript finalizing the fully edited mRNA transcription

Describe the pathway for A to I RNA Editing

First, we use A to I RNA Editing to edit a RNA strand with a wrong nucleotide

Pathways for post transcriptional controls

Describe pathways of regulation of nuclear export with both late and early HIV synthesis

Early HIV Synthesis

Rev & other early viral proteins synthesis

only fully spliced RNAs are exported with Rev, Tat & Nef

~ Rev protein interacts with nuclear export receptor

In late stage unspliced RNA can be exproted

Where is signalling typically located on in mRNA

3’ end

How does mRNA get localized?

Translation is usually blocked until it is localized properly;

RNAs bind to protiens at the 3’ end of RNA to so the RNA does not get in the way of synthesis

Ways for mRNA localization

1. Direct transport on cytoskeleton

2. Random diffusing and trapping

3. Generalized degradation in combination with local protection

Negative translational control example

Sequence-specific RNA-binding protein

What were the two major hypotheses for the number of codons coding for proteins and how was the answer determined?

The major hypotheses were that codons were coded with an odd number or an even number of codons

If there was an even number of codons then= resulting peptide would be homopolypeptide

If there was an odd number of codons then = repeating dipeptide

They found a poly(Serine-leucine) after translating a poly(U) to make polyphenylalanine

Translation of poly(UUC)

if the number of bases in codons was three or a multiple of three, a homopolypeptide

Polyphenylalanine, polyserine, polyleucine

Yielded poly(tyrosine-leucine-serine-isoleucine)

UAU