The present paper explores aspects of similarity and difference between the generic structure of research letters’ abstracts (henceforth RLsA) and research articles’ abstracts (henceforth RAsA). It aims at investigating and documenting the different rhetorical patterns of 19 RLsA and 19 RAsA in order to identify if there is any unique shared way to write them, determine the most publishable way of writing this genre, and detect any possibility of generic overlap between the two genres. Melliti (2016, 2017) CARL model has been adopted to identify the kind, frequency, and overlap of moves in RLsA and RAsA of the Journal Nature. The results indicate that although the RAs are longer than the RLs, the number of sentences in the RLsA is more than the RAsA. Results show also that there are fundamental as well as expendable sets of keys in both genres. The study succeeded also in identifying the number of sentences required to write a publishable research letter abstract and research article abstract in the field of biology. These findings have interesting implication on teaching academic writing and teaching English for publication purposes.