And now this DNA can be used to synthesize the proteins of interest. Now, a common type of retrovirus that we use when we're dealing with mouse cells is the Maloney urenne leukemia virus. And this is used because it can accept DNA molecules as large as 6000 nucleotides in length. Now, the final method we're going to focus on briefly is known as transfection with calcium phosphate. And once again, transfection means the injection of that DNA molecule without actually using any type of viral agent. Now, what we do is we basically create a solution of calcium chloride DNA.