, , and  have demonstrated . . .
Use "in " instead of "in Wiliams et al."
The oncogene jun has presently become one of the best-known oncogenes because of its ability to act as a transcription factor . One study  examined the mRNA levels of jun C, jun B and jun D in various mouse tissues and concluded that each of these genes is expressed independently in different tissues and that they may play a role in growth, development and cellular differentiation.
 F. Cavalieri, T. Ruscio, R. Tinoco, S.
Benedict, C. Davis, and P. K. Vogt,
"Isolation of three new avian sarcoma
viruses: ASV9, ASV17, and ASV 25,"
Virology, vol. 143, pp. 680-683, 1985.
 S. I. Hirai, R. P. Ryseck, F. Mechta, R.
Bravo, M. Yaniv, "Characterization of
jun D: a new member of the jun
protooncogene family," Embo Journ., vol.
8, pp. 1433-1438, 1989.
The results presented in this report show that mammary tissues from mice, rats, and humans, contain constitutive levels of jun B transcripts. This is not surprising since in a previous survey that did not include mammary tissue, jun B was found to be present in a variety of mouse tissues .
--Taniya Sarkar, Wei Zhao, and Nurul H. Sarkar, "Expression of Jun Oncogene in Rodent and Human Breast Tumors," World Wide Web Journal of Biology