When amplifying a full-length gene (around 1.5 kb) from cDNA using primers with varying lengths (24-28 nucleotides) and a melting temperature (Tm) of 62°C, it's important to design a PCR profile that optimizes the amplification process. Here's a suggested PCR profile:

Additional Considerations:

• Primer Design: Ensure that the primers are designed to have similar melting temperatures (Tm). The Tm of the primers can affect the efficiency of PCR.
• PCR Optimization: If the initial PCR does not yield the desired product, consider optimizing reaction conditions, such as primer concentration, MgCl2 concentration, and annealing temperature.
• PCR Clean-up: After successful amplification, consider using a PCR purification kit to remove any remaining primers or nucleotides before downstream applications.

Remember that the optimal PCR conditions may need to be determined empirically, and some degree of optimization might be necessary based on the specifics of your reaction. Running a gradient PCR can be particularly useful in finding the optimal annealing temperature for your specific primer pairs.

Generally, the normal PCR profile works perfectly for such amplifications. You did not mention the polymerase you used. If any HF polymerase (Q5/Phusion etc) is available in your lab, proceed with it once per the manufacturer's instructions. Otherwise, you need to recheck your primers, say for GC content etc. Generally, 1.5 kb amplicon size is not an issue.

I am using Emerald GT PCR mastermix that contain Taq as polymerase