Page 69 - 72_04

An. R. Acad. Nac. Farm., 2006, 72: 611-627

Artículo original

Heme responsiveness in vitro is a common
feature shared by the eukaryotic initiation

factor 2a kinase family

Recibido el 24 de noviembre de 2006

SATURNINO HERRERO +, JUAN JOSÉ BERLANGA,
ISABELA ALONSO y CÉSAR DE HARO *

Centro de Biología Molecular «Severo Ochoa»,
Consejo Superior de Investigaciones Científicas,

Universidad Autónoma de Madrid,
Cantoblanco, 28049 Madrid (Spain)

ABSTRACT

Four distinct eukaryotic initiation factor 2a (eIF2a) kinases phosphorylate eIF2a
at Ser-51 and regulate protein synthesis in response to cellular stress conditions.
This kinase family includes the hemin-regulated inhibitor (HRI); the double-
stranded RNA-dependent kinase (PKR); the GCN2 protein kinase; and the
endoplasmic reticulum-resident kinase (PERK). HRI mediates protein synthesis
inhibition in heme-deficient reticulocyte lysates. Although HRI contains two
putative heme regulatory motifs (HRMs) that are not present in other eIF2a kinases,
the significance of these motifs in heme regulation is not clear. In fact, it had been
characterized two novel eIF2a kinases from Schizosaccharomyces pombe that lacked
any of the HRMs, but were sensitive to heme regulation in vitro. To investigate the
importance of different regions in the regulation of HRI by heme, specific HRI
mutants were generated, and kinase activities and heme responsiveness were
analyzed in vitro. Mutational analysis indicated that the heme regulatory motifs

* Corresponding author: César de Haro, Centro de Biología Molecular «Severo
Ochoa», CSIC-UAM, Facultad de Ciencias, Cantoblanco, 28049 Madrid (Spain).

Phone: 34-91-4978432. Fax: 34-91-4974799. Email: cdeharo@cbm.uam.es
+ Present address: Institute of Applied Biosciences, Dept. of Applied Microbiology,
University of Karlsruhe, Germany.
Abbreviations: HRM, heme regulatory motif; SEK1 & SEK2, S. pombe eIF2a kinases.

611