While I agree that this plant would commonly be called "nightshade", I don't think it is Atropa belladonna. Looking at the line drawing on the referenced wikipedia page, the calyx of Atropa is much larger on the fruit than that of the fruits pictured here. This looks more like Solanum dulcamara, a climbing nightshade that has naturalized here in N. America. Here's the wiki page for S. dulcamara: http://en.wikipedia.org/wiki/Solanum_dulcamara. Look at where the stem meets the fruit - the lobes there are the calyx.
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