The Department of Justice is preparing a lawsuit against Wells Fargo, the nation’s largest home mortgage lender, for allegedly preying upon African American borrowers during the housing bubble and steering them into high-cost subprime loans, according to three people with direct knowledge of the probe. The company, the fourth-largest U.S. bank by assets, is currently embroiled in pre-lawsuit negotiations with the Justice Department in hopes it will settle the accusations and avoid a public lawsuit, these people said.