Chlamydomonas
629
CYB
CYB
dum
-1
deletion
ND4
ND5
ND2
ND1 RTL
ND6 W Q
M
C. smithii
C. reinhardtii
65
7
84
4
3
12
1
3a
2a
2b
3b
COl
CYB
ORF
a
HE BB
X
XH
H
rRNA large
rRNA small
Fig. 4
Physical map of the mitochondrial
genomes of
C. reinhardtii
and
C. smithii
. Genes
for mitochondrial proteins: CYB, cytochrome
b
;
COI, subunit I of cytochrome oxidase; RTL,
reverse transcriptase–like protein; ND 1–6,
subunits of NADH dehydrogenase. The
dispersed arrangement of the ribosomal RNA
genemodu
lesisshown;W,Q,Maregenesof
tRNA Trp, Gln, Met respectively. Restriction site
polymorphisms are indicated for
Bam
HI (B),
Eco
RI (E),
Hpa
I(H)
,and
Xba
I(X).
α
refers to the
intron within the cytochrome
b
gene in
C. smithii
that contains an open reading frame (ORF).
Arrows indicate direction of transcription.
(Reproduced with permission from E.H. Harris,
Genetic Maps
, Vol. 6, Cold Spring Harbor Press,
Plainview, NY, 1993, pp. 2157–3169.)
mitochondrial cytochrome
b
gene of
C.
smithii
, which is interfertile with
C. rein-
hardtii
, contains a mobile group I intron
that has properties similar to those of the
chloroplast ribosomal intron described in
Sect. 2.2. The mitochondrial genomes of
C. eugametos
and
C. moewusii
consist re-
spectively of 24 and 22 kb circular DNA
molecules that are colinear with one an-
other. Although these two mitochondrial
genomes appear to contain the same set
of protein-coding genes as the mitochon-
drial DNA of
C. reinhardtii
,thegenesare
strikingly different in their organization.
Mutants with deletions in the apoc-
ytochrome
b
gene have been isolated
and characterized. These mutants require
light for growth and are unable to grow
on acetate medium in the dark, indicat-
ing that cytochrome
b
is dispensable in
the light. Mitochondrial mutants resistant
to the respiratory inhibitors myxothia-
zol and mucidin have been shown to
carry point mutations in the cytochrome
b
gene.
3
Recent Technical Advances
A major breakthrough in the area of
molecular studies on
Chlamydomonas
was
the establishment of reliable methods for
transformation of the nuclear, chloroplast,
and mitochondrial compartments, and the
establishment of a large EST collection.
3.1
Nuclear Transformation
Nuclear transformation can be easily per-
formed with cell wall–deFcient
C. rein-
hardtii
mutants by vortexing the cells with
glass beads and DNA or by electroporation.
Transformation of the walled strains can
also be achieved with the same techniques
after removing the wall with autolysin, a
glycoprotein that is secreted when gametes
of both mating types are mixed together.
The most widely used host strains are
arg7
, deFcient in argininosuccinate 1yase,
and
nit-1
, deFcient in nitrate reductase.
previous page 1303 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online next page 1305 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online Home Toggle text on/off