beta actin is a type of cell skeleton protein.Its gene is a house keeping gene.In most of cells，beta actin，such as human skeleton，is expressed in a certain level.THat is the reason that people use beta-actin as the criteria of cell numbers.But numerious experiments demonstrated that beta-actin expression is not constant as its previously described，such as under the circumistance of cell starvation and growth signal stimulation，beta-actin expression is either upregulated or downregulated.Therefore，if you use beta-actin as internal control in Western Blot，you have to think about these circumistance，as though beta-actin is the most popular protein sign to be as internal control.
内容来源：生物资料网，如果侵权麻烦联系网站工作人员删除！
