16
G. Jansen et al.
mutations have similar effects on signaling activity. It was previously
described for odr-3, also a Ga subunit, that overproduction resulted in
the same defect of odor perception as gene loss did (Roayaie et al.
1998). Alternatively, loss- and gain-of-function mutations might have
opposite effects, as was found for gpa-2 and -3 (Zwaal et al. 1997). In
cases where loss-of-function mutations may exhibit little phenotype due
to redundancy, gain-of-function mutants may sometimes be more informative.
Taken together, these studies lead us to conclude that three quarters
of the G protein a subunits of C. elegans act in perception: they are
expressed in chemosensory neurons and mutations affect chemoattraction or aversion behavior (Jansen et al. 1999).
2.2 Results and Discussion
2.2.1 The C. elegans Genome Contains 20 Ga Genes
The C. elegans genomic sequence was screened using previously identified Ga gene sequences as query. This identified 20 G protein a subunit
genes, named goa-I, gsa-I, egl-30, gpa-1 to -16, and odr-3. Most Ga
genes can be found on chromosome I or V (Fig. 1). There is a cluster of
six Ga genes on chromosome V, spread over 4.5 map units. Four of
them are quite close together, within 0.5 map units, of which gpa-B and
-9 are only approximately 6 kb apart. No Ga genes have been identified
on chromosome III.
The predicted amino acid sequences of all C. elegans Ga genes were
aligned and compared to representatives of the four mammalian classes:
G/Goa, Gsa, Gqa, and G12a (Fig. 2). The overall structure, a GTPase
domain joined through two linker peptides to an a-helical domain,
seems to be conserved between these Ga subunits. There are however
substitutions of presumed key amino acid residues in gpa-5, -11, -13,
and -14. How these alterations affect G-protein function is unknown.
The alignment showed that there is only one homologue for each of
the four main vertebrate classes of Ga genes (Fig. 2); Gj/Goa: goa-1
(Lochrie et al. 1991), Gsa: gsa- I (Park et al. 1997), Gqa: egl-30 (Brundage et al. 1996), and G12a: gpa-12. As the 16 other Ga subunits cannot
G. Jansen et al.
mutations have similar effects on signaling activity. It was previously
described for odr-3, also a Ga subunit, that overproduction resulted in
the same defect of odor perception as gene loss did (Roayaie et al.
1998). Alternatively, loss- and gain-of-function mutations might have
opposite effects, as was found for gpa-2 and -3 (Zwaal et al. 1997). In
cases where loss-of-function mutations may exhibit little phenotype due
to redundancy, gain-of-function mutants may sometimes be more informative.
Taken together, these studies lead us to conclude that three quarters
of the G protein a subunits of C. elegans act in perception: they are
expressed in chemosensory neurons and mutations affect chemoattraction or aversion behavior (Jansen et al. 1999).
2.2 Results and Discussion
2.2.1 The C. elegans Genome Contains 20 Ga Genes
The C. elegans genomic sequence was screened using previously identified Ga gene sequences as query. This identified 20 G protein a subunit
genes, named goa-I, gsa-I, egl-30, gpa-1 to -16, and odr-3. Most Ga
genes can be found on chromosome I or V (Fig. 1). There is a cluster of
six Ga genes on chromosome V, spread over 4.5 map units. Four of
them are quite close together, within 0.5 map units, of which gpa-B and
-9 are only approximately 6 kb apart. No Ga genes have been identified
on chromosome III.
The predicted amino acid sequences of all C. elegans Ga genes were
aligned and compared to representatives of the four mammalian classes:
G/Goa, Gsa, Gqa, and G12a (Fig. 2). The overall structure, a GTPase
domain joined through two linker peptides to an a-helical domain,
seems to be conserved between these Ga subunits. There are however
substitutions of presumed key amino acid residues in gpa-5, -11, -13,
and -14. How these alterations affect G-protein function is unknown.
The alignment showed that there is only one homologue for each of
the four main vertebrate classes of Ga genes (Fig. 2); Gj/Goa: goa-1
(Lochrie et al. 1991), Gsa: gsa- I (Park et al. 1997), Gqa: egl-30 (Brundage et al. 1996), and G12a: gpa-12. As the 16 other Ga subunits cannot