Contents

12 November 1999
Vol 286, Issue 5443

About The Cover

Cover image expansion

COVER This Xenopus laevis embryo (1 mm) demonstrates that expression of constitutively active p90 ribosomal S6 kinase is sufficient to induce metaphase arrest. Therefore, this kinase is the only substrate of the mitogen-activated protein kinase pathway required for cytostatic factor activity, which arrests the cell cycle of vertebrate eggs and embryos at metaphase. See page 1365 [Image: S. D. Gross]