284
P. TSIBOLI et aI.
Zinc-fingers have been implicated in nucleic acid binding (Kohn et al. 1997).
What is the possible role of the zinc-finger in the S14 ribosomal protein? One
answer might be the participation of the structure in the binding of rRNA. The
C2H2 domain of the transcription factor IlIA (TFIlIA) has been shown to bind
5S rRNA (Travers 1993) and the C3H domain of the human immunodeficiency
virus gag protein is involved in the packaging of the RNA genome of the virus
(Demene et al. 1994). On the other hand, zinc-finger motifs of the C4 variety,
such as those of the hormone receptor and transcription factor GATA (Chan et al.
1993), have been primarily implicated in DNA binding. In the above mentioned
proteins, zinc-fingers are in the form of tandem repeats whereas ribosomal proteins only contain a single motif. However, it has been recently shown by Pedone
et al. (Pedone eet al. 1996) that the combination of an amino-terminal basic
region with a single C2H2 zinc-finger in the GAGA protein is sufficient for high
affinity DNA binding domain.
An interaction between the 16S rRNA and the S14 has been proven. In Bacillus
stearothermophiIus S14 (BstS14) Lys16 has been cross-linked to 16S rRNA proving it to be in direct contact to the RNA (Urlaub et aI. 1995). Lys16 of BstS14 is
homologous to Lys17 in TthS14 (Fig. 20.8) and is in close proximity to the zincfinger motif. S14 from E. coli protects several base pairs in the 990-1050 nt
region of 16S rRNA from chemical modification (Stern et al. 1989). Still, the zincfinger might not be absolutely required for the rRNA-protein interaction. The E.
coli S 14 lacks the zinc-finger motif. Only one of the four cysteines has been conserved. On the other hand, both the sequence which corresponds to the linker
region of the zinc-finger motif (Fig. 20.8) and the sequence of the rRNA domain
known to interact with S14 are highly conserved (Noller et al. 1995, and Stern et
al. 1988). Therefore, the interaction might take place between the linker region
and the rRNA and consequently the zinc-finger would not be absolutely required
for the assembly and function of the 30S subunit. It might be that it is only a "fossil" of the function of the ancestral molecule, which was recruited into the ribosome and evolved into S14. The existence of the zinc-finger in the S14 from
archaea and in the related S29 from eucaryotes (Fig. 20.8) points to an ancient
origin (Wool et aI. 1995).
The question remains as to the reason why several organisms have retained
this structure in S14. One possible reason is that certain organisms, such as the
thermophilic Thermus thermophilus might need the extra stabilization of the
rRNA structure by the interaction with the zinc-finger. A second possibility is
that the zinc-finger has an alternate functionality. The S27 ribosomal protein
from human, which contains a similar C4 zinc-finger, has been shown to interact
specifically with cap elements and to act in the stimulation of several genes in
Fig. 20.S. Alignment of the ribosomal protein TthS14 (Tsiboli and Choli 1995), using the PC-Gene
program, with its counterparts from the following organisms, as well as with the ribosomal proteins
S29 and S27: B. stearothermophilus (Herfurth 1992), B. subtilis (Henkin et al. 1989), T. aquaticus
(Jahn et al. 1991), M. vanniellii (Auer et al. 1989), M. capricolum (Ohkubo et al. 1987), E. coli (Yagushi
et al. 1983), Vicia faba (Wahleithner and Wolstenholme 1988), Oryzia sativa (Cote and Wu 1988), S.
cerevisiae (Larkin et al. 1987), H. marismortui (Scholzen and Arndt 1991), Human S29 (Frigerio et al.
1995), Entamoeba histolytica S27 (Stanley and Li 1992)
P. TSIBOLI et aI.
Zinc-fingers have been implicated in nucleic acid binding (Kohn et al. 1997).
What is the possible role of the zinc-finger in the S14 ribosomal protein? One
answer might be the participation of the structure in the binding of rRNA. The
C2H2 domain of the transcription factor IlIA (TFIlIA) has been shown to bind
5S rRNA (Travers 1993) and the C3H domain of the human immunodeficiency
virus gag protein is involved in the packaging of the RNA genome of the virus
(Demene et al. 1994). On the other hand, zinc-finger motifs of the C4 variety,
such as those of the hormone receptor and transcription factor GATA (Chan et al.
1993), have been primarily implicated in DNA binding. In the above mentioned
proteins, zinc-fingers are in the form of tandem repeats whereas ribosomal proteins only contain a single motif. However, it has been recently shown by Pedone
et al. (Pedone eet al. 1996) that the combination of an amino-terminal basic
region with a single C2H2 zinc-finger in the GAGA protein is sufficient for high
affinity DNA binding domain.
An interaction between the 16S rRNA and the S14 has been proven. In Bacillus
stearothermophiIus S14 (BstS14) Lys16 has been cross-linked to 16S rRNA proving it to be in direct contact to the RNA (Urlaub et aI. 1995). Lys16 of BstS14 is
homologous to Lys17 in TthS14 (Fig. 20.8) and is in close proximity to the zincfinger motif. S14 from E. coli protects several base pairs in the 990-1050 nt
region of 16S rRNA from chemical modification (Stern et al. 1989). Still, the zincfinger might not be absolutely required for the rRNA-protein interaction. The E.
coli S 14 lacks the zinc-finger motif. Only one of the four cysteines has been conserved. On the other hand, both the sequence which corresponds to the linker
region of the zinc-finger motif (Fig. 20.8) and the sequence of the rRNA domain
known to interact with S14 are highly conserved (Noller et al. 1995, and Stern et
al. 1988). Therefore, the interaction might take place between the linker region
and the rRNA and consequently the zinc-finger would not be absolutely required
for the assembly and function of the 30S subunit. It might be that it is only a "fossil" of the function of the ancestral molecule, which was recruited into the ribosome and evolved into S14. The existence of the zinc-finger in the S14 from
archaea and in the related S29 from eucaryotes (Fig. 20.8) points to an ancient
origin (Wool et aI. 1995).
The question remains as to the reason why several organisms have retained
this structure in S14. One possible reason is that certain organisms, such as the
thermophilic Thermus thermophilus might need the extra stabilization of the
rRNA structure by the interaction with the zinc-finger. A second possibility is
that the zinc-finger has an alternate functionality. The S27 ribosomal protein
from human, which contains a similar C4 zinc-finger, has been shown to interact
specifically with cap elements and to act in the stimulation of several genes in
Fig. 20.S. Alignment of the ribosomal protein TthS14 (Tsiboli and Choli 1995), using the PC-Gene
program, with its counterparts from the following organisms, as well as with the ribosomal proteins
S29 and S27: B. stearothermophilus (Herfurth 1992), B. subtilis (Henkin et al. 1989), T. aquaticus
(Jahn et al. 1991), M. vanniellii (Auer et al. 1989), M. capricolum (Ohkubo et al. 1987), E. coli (Yagushi
et al. 1983), Vicia faba (Wahleithner and Wolstenholme 1988), Oryzia sativa (Cote and Wu 1988), S.
cerevisiae (Larkin et al. 1987), H. marismortui (Scholzen and Arndt 1991), Human S29 (Frigerio et al.
1995), Entamoeba histolytica S27 (Stanley and Li 1992)