Homologous recombination between microinjected SV40 DNA fragments and endogenous SV40 DNA in COS7 cells was analysed by immunofluorescence staining and DNA blotting. Time course experiments revealed that recombination between the transferred (trans) DNA and the chromosomal DNA occurred about 8 hours after microinjection with high efficiency in a gene dose independent fashion. Deletions of up to 1018 basepairs (bp) within the early or the late SV40 region were efficiently repaired after the transfer of linear but not of circular DNA molecules. A 22 bp homology between the trans DNA and the endogenous DNA was sufficient to initiate recombination but 14 nonhomologous bp at one open end of the SV40 DNA fragments hindered gap repair.

series of enantiomerically pure bis(myrtanyl)tin compounds, cis-Myr 2 SnX 2 (1, X ) Ph; 3, X ) Cl; 5, X ) H) and trans-Myr 2 SnX 2 (2, X ) Ph; 4, X ) Cl; 6, X ) H) were prepared starting from (-)-1S-βpinene and characterized by multinuclear NMR spectroscopy and in case of 3 and 4 also by X-ray crystallography. The reduction of 3 and 4 with Mg selectively produced pentastannane rings, cyclo-(cis-Myr 2 Sn) 5 ( 7) and cyclo-(trans-Myr 2 Sn) 5 ( 8), while the dehydropolymerization of 5 and 6 produced a mixture of polystannanes, poly(cis-Myr 2 Sn) n (9) or poly(trans-Myr 2 Sn) n (10), and oligomers that could not be separated. The pentastannane rings gave rise to UV absorptions at λ max 219 and 217 nm, which were assigned to σ f σ* transitions of the Sn-Sn bonds. Due to the increased σ-electron delocalization, the polystannanes 9 and 10 show red-shifted UV absorptions at λ max 416 and 417 nm. The CD spectra of the polystannanes 9 and 10 reveal a positive cotton effect at λ max 422 and 425 nm, consistent with the idea that the chiral information is transferred from the UV-inactive myrtanyl groups to the polymer backbone, which most likely adopts a helical conformation with the right-handed screw sense being in excess.

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