Transcript Chapter 21 The Genetic Control of Animal Development

What
Whatdoes
doesthe
theword
wordPromoter
Promotermean?
mean?
It is the place at which RNA Pol II binds.
But the word is incorrectly used to describe
Enhancers plus Promoter.
Initiation by RNA Polymerase II
TFIID recognition site is TATAA
How often is this site found in the
genome? 1/45
Once every 1000 nucleotides 109 nucleotides or 106 times
Transient transfection
More Cells
But on a per cell
Basis expression levels of -gal
is about the same
Stable transfection
Recruitment Model
The Differentiation of
Vertebrate Immune Cells
 In the immune system, two types of cells participate
directly in defense against pathogens.
 Plasma B cells produce and secrete immunoglobulins
(antibodies), and killer T cell produce membranebound proteins that act as receptors for various
substances.
 B cell antibodies and T cell receptors bind to specific
antigens. A cell must make many varieties of these
proteins because there are many potential
pathogens.
An Antigen-Antibody Complex
Structure of an Antibody Molecule
Human Antibody Genes
Two light chain loci: the  on
chromosome 2 and  on
chromosome 22
One heavy chain locus on
chromosome 14.
Each locus consists of a long array
of gene segments.
Gene Segments for a Kappa
Polypeptide
1.
An LV gene segment, encoding a leader peptide,
which is removed later, and the N-terminal 95
amino acids of the variable region of the kappa light
chain. (76 gene segments in humans; 40 of these
are functional)
2.
A J gene segment, encoding the last 13 amino
acids of the variable region of the kappa light chain.
(5 gene segments in humans)
3.
A C gene segment, encoding the constant region
of the kappa light chain. (1 gene segment in
humans)
The Kappa Locus
During B cell development, the kappa light
chain gene that will be expressed is
assembled from one LV segment, one J
segment, and the C segment by somatic
recombination.
 Segment joining is mediated by recombination signal
sequences adjacent to each gene segment by a
protein complex including RAG1 and RAG2
(recombination activating gene proteins 1 and 2).
Many Different Antibodies Can
Be Produced
40 LV segments  5 J segments  1 C segment
= 200 kappa light chains.
Recombination of gene segments can create
120 lambda light chains and 6600 different
heavy chains.
Combinatorial assembly of these allows
production of 2,112,000 different antibodies.
Even more antibodies are possible due to
variation in recombination sites and
hypermutability of the variable regions.
Evidence for DNA Rearrangement
During Immune Cell Differentiation
http://www.youtube.com/watch?v=AxIMmNByqtM
Conserved sequences in Bold
Gene
Conversion
of HML alpha
or HMR a
Loci into MAT locus
Figure 19.22
Copyright © 2010 Academic Press Inc.
HMR a
HML alpha
HMR a
HML alpha