Tài liệu Báo cáo khoa học: Stimulation of poly(A) synthesis by Escherichia coli poly(A)polymerase I

Stimulation of poly(A) synthesis by Escherichia coli

poly(A)polymerase I is correlated with Hfq binding to

poly(A) tails

Marc Folichon, Fre´de´ric Allemand, Philippe Re´gnier and Eliane Hajnsdorf

UPR CNRS 9073, conventionne´e avec l’Universite´ Paris 7 – Denis Diderot, Institut de Biologie Physico-Chimique, Paris, France

Host factor I (Hfq) is an abundant protein of

Escherichia coli, which was first identified as a host

factor required for the replication of Qb bacterio￾phage [1]. It has then been established that disrup￾tion of the hfq gene causes pronounced pleiotropic

phenotypes in uninfected E. coli [2] and that in other

bacteria Hfq permits the adaptation to multiple envi￾ronmental stresses [3,4].

There is now an accumulation of data that shows

Hfq is an RNA-binding protein that is associated with

RNA replication, translation and stabilization [5–8].

In the case of phage Qb replication, Hfq acts directly

by bringing into close proximity the 3¢ terminal and

internal regions of the genomic RNA [9]. Hfq was also

reported to weaken base-pairing in stem loops of

OxyS sRNA, to mask the ribosome binding site of

ompA mRNA [10], to protect several RNAs from deg￾radation by ribonucleases [11,12] and to assist many

sRNAs in their activity [5,13–16]. In this latter case, it

was shown that Hfq facilitates base-pairing between

small regulatory RNAs and their mRNA target

[17,18]. These properties and its capacity to rescue a

splicing defective intron from a ‘folding trap’ led to

the proposal that Hfq is an RNA chaperone acting at

many different steps of RNA metabolism [15,19–21].

In addition, the presence of a characteristic Sm fold

and its organization in a crown-shaped homo-hexamer

proved that Hfq belongs to the Sm-like protein family

[18,22–24] whose members are involved in many

RNA–RNA and RNA–protein transactions. Finally,

Hfq was also recently reported to interact with ribo￾somal protein S1 and RNA polymerase, to exhibit an

Keywords

E. coli; Hfq protein; poly(A)-polymerase I;

polynucleotide phosphorylase; RNA–protein

interaction

Correspondence

E. Hajnsdorf, UPR CNRS 9073,

conventionne´e avec l’Universite´ Paris

7 – Denis Diderot, Institut de Biologie

Physico-Chimique, 13 rue Pierre et Marie

Curie, 75005 Paris, France

Fax: +33 1 58 41 50 20

Tel: +33 1 58 41 51 26

E-mail: [email protected]

(Received 16 September 2004, revised 15

November 2004, accepted 16 November

2004)

doi:10.1111/j.1742-4658.2004.04485.x

The bacterial Lsm protein, host factor I (Hfq), is an RNA chaperone

involved in many types of RNA transactions such as replication and stabil￾ity, control of small RNA activity and polyadenylation. In this latter case,

Hfq stimulates poly(A) synthesis and binds poly(A) tails that it protects

from exonucleolytic degradation. We show here, that there is a correlation

between Hfq binding to the 3¢ end of an RNA molecule and its ability to

stimulate RNA elongation catalyzed by poly(A)polymerase I. In contrast,

formation of the Hfq–RNA complex inhibits elongation of the RNA by

polynucleotide phosphorylase. We demonstrate also that Hfq binding is

not affected by the phosphorylation status of the RNA molecule and

occurs equally well at terminal or internal stretches of poly(A).

Abbreviations

Hfq, host factor I; PAP I, poly(A)polymerase; PNPase, polynucleotide phosphorylase.

454 FEBS Journal 272 (2005) 454–463 ª 2004 FEBS