MOLECULAR EVOLUTION OF THE AC DS TRANSPOSABLE-ELEMENT FAMILY IN PEARL-MILLET AND OTHER GRASSES/

We report an Ac-like sequence from pearl millet (Pennisetum glaucum) a nd deletion derivative Ac-like sequences from pearl millet and another grass species, Bambusa multiplex. Sequence relationships between the pearl millet and maize Ac elements suggest the Ac/Ds transposable-elem ent family is ancient. Further, the sequence identity between the Bamb usa Ac-like sequence and maize Ac implies that the Ac/Ds transposable- element family has been in the grass family since its inception. The A c-Iike sequences reported from pearl millet and maize Ac are statistic ally heterogeneous in pair-wise distance comparisons to each other. Ye t, we are unable to discriminate between differential selection or ect opic exchange (recombination and conversion) between nonidentical tran sposable element homologues, as the cause of the heterogeneity. Howeve r, the more extreme heterogeneity exhibited between the previously des cribed pearl millet element and maize Ac seems likely to derive from e ctopic exchange between elements with different levels of divergence.