NanoString Technologies Inc. plans to offer 4.5 million shares in an underwritten public offering.

Seattle-based NanoString will sell 2.5 million common shares, while private equity firm Clarus Lifesciences II LP, a NanoString stockholder, will sell 2 million shares. NanoString will not receive proceeds from the sale by Cambridge, Mass.-based Clarus.

Underwriters will have an option to buy up to 675,000 additional common shares.

NanoString plans to use net proceeds for working capital and general corporate purposes.

J.P. Morgan, UBS Investment Bank and Cowen are acting as joint book-running managers, with Baird acting as lead manager for the offering.

NanoString Technologies is a provider of life science tools for translational research and molecular diagnostic products.