translation, with the most prominent species (~85%) of cellular RNA being rRNA. As a result, this is the most immediately visible species when RNA is analyzed via electrophoresis and is thus used for determining RNA quality (see Computation, below). rRNA comes in various sizes, with those in mammals belonging to the sizes 5S, 18S, and 28S. The 28S and 5S rRNAs form the large subunit and the 18S forms the small subunit of the ribosome, the molecular machinery responsible for synthesizing proteins. Applications RNases are ubiquitous and can often contaminate and subsequently degrade RNA samples in the laboratory, so RNA integrity can very easily be compromised, leading to a number of laboratory techniques designed to eliminate their impact. However, these methods are not fool-proof, and so samples can still be degraded, necessitating a method of measuring RNA integrity to ensure the trustworthiness and reproducibility of molecular assays, as RNA integrity is critical for proper results in gene expression studies, such as microarray analysis, Northern blots, or quantitative real-time PCR (qPCR). RNA that has been degraded has a direct impact on calculated expression levels, often leading to significantly decreased apparent expression. qPCR and similar techniques are very expensive, taking a good deal of both time and money, so continuing research being undertaken to decrease the cost while maintaining qPCR's accuracy and reproducibility for gene expression and other applications. RIN assessment allows a scientist to evaluate an experiment's trustworthiness and reproducibility before incurring substantial costs in performing the gene expression studies. RIN is a standard method of measuring RNA integrity and can be used to evaluate the quality of RNA produced by new RNA isolation techniques. Development As RNA integrity has long been known to be a problem in molecular biology studies, there are a few methods that have been used historically to determine the integrity of RNA. The most popular has long been agarose gel electrophoresis with ethidium bromide staining, allowing one to visualize the bands from the rRNA peaks. The height of the 28S and 18S bands can be compared to each other, with a 2:1 ratio indicating non-degraded RNA. While this method is very cheap and easy, there are several issues with this method, primarily its subjectivity, leading to inconsistent, non-standardized RNA quality assessments, and the large amounts of RNA that are needed to visualize it on an agarose gel, which can be problematic if there is not much