WhenisolatingRNA,ithelpstohavearoughideaofhowmuchtotalorpoly(A)RNAcanberecoveredfromagivenamountoftissueorcells.ItisalsobeneficialtoknowroughexpressionlevelsforraretomoderatelyabundanttranscriptswhenperformingNorthernanalysisorRPAs,e.g.inordertosetupameaningfulstandardcurveforabsolutequantitation,ortoknowhowlongofanexposureisreasonable.Thesenumbersprovideapointofreferenceagainstwhichexperimentalproceduresandresultscanbechecked.Tables1and2providegeneralguidelinesforestimatingRNAyieldsfromavarietyofcellsandtissues.RememberthatRNAyieldsfromanalogoustissuesindifferentorganismscanalsovary: