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Proc Natl Acad Sci U S A. 2013 Jun 25;110(26):10854-9. doi: 10.1073/pnas.1302592110. Epub 2013 Jun 10.

Hypoxic survival requires a 2-on-2 hemoglobin in a process involving nitric oxide.

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  • 1Fakultät für Biologie und Biotechnologie, Lehrstuhl für Biochemie der Pflanzen, AG Photobiotechnologie, Ruhr Universität Bochum, 44801 Bochum, Germany. anja.hemschemeier@rub.de


Hemoglobins are recognized today as a diverse family of proteins present in all kingdoms of life and performing multiple reactions beyond O2 chemistry. The physiological roles of most hemoglobins remain elusive. Here, we show that a 2-on-2 ("truncated") hemoglobin, termed THB8, is required for hypoxic growth and the expression of anaerobic genes in Chlamydomonas reinhardtii. THB8 is 1 of 12 2-on-2 hemoglobins in this species. It belongs to a subclass within the 2-on-2 hemoglobin class I family whose members feature a remarkable variety of domain arrangements and lengths. Posttranscriptional silencing of the THB8 gene results in the mis-regulation of several genes and a growth defect under hypoxic conditions. The latter is intensified in the presence of an NO scavenger, which also impairs growth of wild-type cells. As recombinant THB8 furthermore reacts with NO, the results of this study indicate that THB8 is part of an NO-dependent signaling pathway.


gene expression; hypoxia

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