It is possible that single-stranded DNA (ssDNA) contains structural features that resemble the beta-form. Evidence suggesting this comes from electron microscopic length measurements of recA-ssDNA filaments, which indicate DNA in this complex to be stretched one and one-half times. Since synapsis between homologous DNA molecules begins with the invasion of a recA-ssDNA filamentous complex into actively breathing DNA duplex regions, DNA must be both complementary in sequence and structurally compatible for pairing to occur. The presence of a transient single-stranded beta-DNA like form within the premelton could, therefore, play a key role in initiating homologous pairing with the recA-ssDNA complex in this early synaptic step required for genetic recombination.

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